From b552557655d7cde33cd71f56dac99f087c5b5225 Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Sat, 28 Jun 2025 13:41:44 +0300
Subject: [PATCH 01/34] Created an enum for choosing a named pattern.

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../core/pattern/DatePatternConverter.java    | 70 +++++--------------
 .../log4j/core/pattern/NamedPattern.java      | 43 ++++++++++++
 2 files changed, 59 insertions(+), 54 deletions(-)
 create mode 100644 log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index f26a6d54c56..a17453480e2 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -16,14 +16,6 @@
  */
 package org.apache.logging.log4j.core.pattern;
 
-import static java.util.Objects.requireNonNull;
-
-import java.time.format.DateTimeFormatter;
-import java.util.Arrays;
-import java.util.Date;
-import java.util.Locale;
-import java.util.TimeZone;
-import java.util.stream.Collectors;
 import org.apache.commons.lang3.time.FastDateFormat;
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.config.plugins.Plugin;
@@ -37,6 +29,15 @@
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
+import java.time.format.DateTimeFormatter;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.Locale;
+import java.util.TimeZone;
+import java.util.stream.Collectors;
+
+import static java.util.Objects.requireNonNull;
+
 /**
  * Converts and formats the event's date in a StringBuilder.
  */
@@ -140,53 +141,14 @@ static String decodeNamedPattern(final String pattern) {
         //   This is the correct behaviour for `SimpleDateFormat`.
         //   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
         //   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
-        final boolean compat = InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED;
-
-        switch (pattern) {
-            case "ABSOLUTE":
-                return "HH:mm:ss,SSS";
-            case "ABSOLUTE_MICROS":
-                return "HH:mm:ss," + (compat ? "nnnnnn" : "SSSSSS");
-            case "ABSOLUTE_NANOS":
-                return "HH:mm:ss," + (compat ? "nnnnnnnnn" : "SSSSSSSSS");
-            case "ABSOLUTE_PERIOD":
-                return "HH:mm:ss.SSS";
-            case "COMPACT":
-                return "yyyyMMddHHmmssSSS";
-            case "DATE":
-                return "dd MMM yyyy HH:mm:ss,SSS";
-            case "DATE_PERIOD":
-                return "dd MMM yyyy HH:mm:ss.SSS";
-            case "DEFAULT":
-                return "yyyy-MM-dd HH:mm:ss,SSS";
-            case "DEFAULT_MICROS":
-                return "yyyy-MM-dd HH:mm:ss," + (compat ? "nnnnnn" : "SSSSSS");
-            case "DEFAULT_NANOS":
-                return "yyyy-MM-dd HH:mm:ss," + (compat ? "nnnnnnnnn" : "SSSSSSSSS");
-            case "DEFAULT_PERIOD":
-                return "yyyy-MM-dd HH:mm:ss.SSS";
-            case "ISO8601_BASIC":
-                return "yyyyMMdd'T'HHmmss,SSS";
-            case "ISO8601_BASIC_PERIOD":
-                return "yyyyMMdd'T'HHmmss.SSS";
-            case "ISO8601":
-                return "yyyy-MM-dd'T'HH:mm:ss,SSS";
-            case "ISO8601_OFFSET_DATE_TIME_HH":
-                return "yyyy-MM-dd'T'HH:mm:ss,SSS" + (compat ? "X" : "x");
-            case "ISO8601_OFFSET_DATE_TIME_HHMM":
-                return "yyyy-MM-dd'T'HH:mm:ss,SSS" + (compat ? "XX" : "xx");
-            case "ISO8601_OFFSET_DATE_TIME_HHCMM":
-                return "yyyy-MM-dd'T'HH:mm:ss,SSS" + (compat ? "XXX" : "xxx");
-            case "ISO8601_PERIOD":
-                return "yyyy-MM-dd'T'HH:mm:ss.SSS";
-            case "ISO8601_PERIOD_MICROS":
-                return "yyyy-MM-dd'T'HH:mm:ss." + (compat ? "nnnnnn" : "SSSSSS");
-            case "US_MONTH_DAY_YEAR2_TIME":
-                return "dd/MM/yy HH:mm:ss.SSS";
-            case "US_MONTH_DAY_YEAR4_TIME":
-                return "dd/MM/yyyy HH:mm:ss.SSS";
+        try {
+            final NamedPattern namedPattern = NamedPattern.valueOf(pattern);
+            return InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ?
+                    namedPattern.getLegacyPattern() :
+                    namedPattern.getNonLegacyPattern();
+        } catch (IllegalArgumentException ignored) { // for Java 22+ it can be changed to `IllegalArgumentException _`
+            return pattern;
         }
-        return pattern;
     }
 
     private static TimeZone readTimeZone(@Nullable final String[] options) {
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
new file mode 100644
index 00000000000..e5de3451b4b
--- /dev/null
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
@@ -0,0 +1,43 @@
+package org.apache.logging.log4j.core.pattern;
+
+@SuppressWarnings("SpellCheckingInspection")
+public enum NamedPattern {
+    ABSOLUTE("HH:mm:ss,SSS", "HH:mm:ss,SSS"),
+    ABSOLUTE_MICROS("HH:mm:ss,nnnnnn", "HH:mm:ss,SSSSSS"),
+    ABSOLUTE_NANOS("HH:mm:ss,nnnnnnnnn", "HH:mm:ss,SSSSSSSSS"),
+    ABSOLUTE_PERIOD("HH:mm:ss.SSS", "HH:mm:ss.SSS"),
+    COMPACT("yyyyMMddHHmmssSSS", "yyyyMMddHHmmssSSS"),
+    DATE("dd MMM yyyy HH:mm:ss,SSS", "dd MMM yyyy HH:mm:ss,SSS"),
+    DATE_PERIOD("dd MMM yyyy HH:mm:ss.SSS", "dd MMM yyyy HH:mm:ss.SSS"),
+    DEFAULT("yyyy-MM-dd HH:mm:ss,SSS", "yyyy-MM-dd HH:mm:ss,SSS"),
+    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,nnnnnn", "yyyy-MM-dd HH:mm:ss,SSSSSS"),
+    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,nnnnnnnnn", "yyyy-MM-dd HH:mm:ss,SSSSSSSSS"),
+    DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS", "yyyy-MM-dd HH:mm:ss.SSS"),
+    ISO8601_BASIC("yyyyMMdd'T'HHmmss,SSS", "yyyyMMdd'T'HHmmss,SSS"),
+    ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS", "yyyyMMdd'T'HHmmss.SSS"),
+    ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS", "yyyy-MM-dd'T'HH:mm:ss,SSS"),
+    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSX", "yyyy-MM-dd'T'HH:mm:ss,SSSx"),
+    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
+    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
+    ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS", "yyyy-MM-dd'T'HH:mm:ss.SSS"),
+    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.nnnnnn", "yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
+    US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS", "dd/MM/yy HH:mm:ss.SSS"),
+    US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS", "dd/MM/yyyy HH:mm:ss.SSS");
+
+    private final String
+            legacyPattern,
+            nonLegacyPattern;
+
+    NamedPattern(String legacyPattern, String nonLegacyPattern) {
+        this.legacyPattern = legacyPattern;
+        this.nonLegacyPattern = nonLegacyPattern;
+    }
+
+    public String getLegacyPattern() {
+        return legacyPattern;
+    }
+
+    public String getNonLegacyPattern() {
+        return nonLegacyPattern;
+    }
+}

From 9d330d494e9b6912296bea169edb86b01b37fb4a Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Sat, 28 Jun 2025 13:50:09 +0300
Subject: [PATCH 02/34] Applied `spotless:apply`

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../core/pattern/DatePatternConverter.java    | 23 ++++++++--------
 .../log4j/core/pattern/NamedPattern.java      | 27 ++++++++++++++-----
 2 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index a17453480e2..ac88a495769 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -16,6 +16,14 @@
  */
 package org.apache.logging.log4j.core.pattern;
 
+import static java.util.Objects.requireNonNull;
+
+import java.time.format.DateTimeFormatter;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.Locale;
+import java.util.TimeZone;
+import java.util.stream.Collectors;
 import org.apache.commons.lang3.time.FastDateFormat;
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.config.plugins.Plugin;
@@ -29,15 +37,6 @@
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
-import java.time.format.DateTimeFormatter;
-import java.util.Arrays;
-import java.util.Date;
-import java.util.Locale;
-import java.util.TimeZone;
-import java.util.stream.Collectors;
-
-import static java.util.Objects.requireNonNull;
-
 /**
  * Converts and formats the event's date in a StringBuilder.
  */
@@ -143,9 +142,9 @@ static String decodeNamedPattern(final String pattern) {
         //   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
         try {
             final NamedPattern namedPattern = NamedPattern.valueOf(pattern);
-            return InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ?
-                    namedPattern.getLegacyPattern() :
-                    namedPattern.getNonLegacyPattern();
+            return InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED
+                    ? namedPattern.getLegacyPattern()
+                    : namedPattern.getNonLegacyPattern();
         } catch (IllegalArgumentException ignored) { // for Java 22+ it can be changed to `IllegalArgumentException _`
             return pattern;
         }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
index e5de3451b4b..a32497046bb 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
@@ -1,3 +1,19 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 package org.apache.logging.log4j.core.pattern;
 
 @SuppressWarnings("SpellCheckingInspection")
@@ -17,16 +33,15 @@ public enum NamedPattern {
     ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS", "yyyyMMdd'T'HHmmss.SSS"),
     ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS", "yyyy-MM-dd'T'HH:mm:ss,SSS"),
     ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSX", "yyyy-MM-dd'T'HH:mm:ss,SSSx"),
-    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
-    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
+    ISO8601_OFFSET_DATE_TIME_HHMM(
+            "yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
+    ISO8601_OFFSET_DATE_TIME_HHCMM(
+            "yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
     ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS", "yyyy-MM-dd'T'HH:mm:ss.SSS"),
     ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.nnnnnn", "yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
     US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS", "dd/MM/yy HH:mm:ss.SSS"),
     US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS", "dd/MM/yyyy HH:mm:ss.SSS");
-
-    private final String
-            legacyPattern,
-            nonLegacyPattern;
+    private final String legacyPattern, nonLegacyPattern;
 
     NamedPattern(String legacyPattern, String nonLegacyPattern) {
         this.legacyPattern = legacyPattern;

From 8f427a0d77fe320914b2c916590068d7035ca228 Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Sat, 28 Jun 2025 14:19:18 +0300
Subject: [PATCH 03/34] Added changelog entry

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../.2.x.x/exported_named_patterns_into_public_enum.xml    | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml

diff --git a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
new file mode 100644
index 00000000000..377bf063178
--- /dev/null
+++ b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="changed">
+  <description format="asciidoc">Exported named-patterns into its own public enum</description>
+</entry>

From b19d830e5c292981e281521c9037f1e1c6173e02 Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Sat, 28 Jun 2025 14:27:24 +0300
Subject: [PATCH 04/34] No need for (another) default hard-coded named pattern

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../logging/log4j/core/pattern/DatePatternConverter.java  | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index ac88a495769..88f4588ab0e 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -49,8 +49,6 @@ public final class DatePatternConverter extends LogEventPatternConverter impleme
 
     private static final String CLASS_NAME = DatePatternConverter.class.getSimpleName();
 
-    private static final String DEFAULT_PATTERN = "yyyy-MM-dd HH:mm:ss,SSS";
-
     private final InstantFormatter formatter;
 
     private DatePatternConverter(@Nullable final String[] options) {
@@ -64,7 +62,9 @@ private static InstantFormatter createFormatter(@Nullable final String[] options
         } catch (final Exception error) {
             logOptionReadFailure(options, error, "failed for options: {}, falling back to the default instance");
         }
-        return InstantPatternFormatter.newBuilder().setPattern(DEFAULT_PATTERN).build();
+        return InstantPatternFormatter.newBuilder()
+                .setPattern(NamedPattern.DEFAULT.getNonLegacyPattern())
+                .build();
     }
 
     private static InstantFormatter createFormatterUnsafely(@Nullable final String[] options) {
@@ -94,7 +94,7 @@ private static InstantFormatter createFormatterUnsafely(@Nullable final String[]
     private static String readPattern(@Nullable final String[] options) {
         return options != null && options.length > 0 && options[0] != null
                 ? decodeNamedPattern(options[0])
-                : DEFAULT_PATTERN;
+                : NamedPattern.DEFAULT.getNonLegacyPattern();
     }
 
     /**

From 3df9d887b21d8d628211eb47f31ea5d1b786ed9e Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Sat, 28 Jun 2025 14:42:10 +0300
Subject: [PATCH 05/34] Fixed small bug

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../org/apache/logging/log4j/core/pattern/NamedPattern.java | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
index a32497046bb..cef77decfb8 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
@@ -33,10 +33,8 @@ public enum NamedPattern {
     ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS", "yyyyMMdd'T'HHmmss.SSS"),
     ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS", "yyyy-MM-dd'T'HH:mm:ss,SSS"),
     ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSX", "yyyy-MM-dd'T'HH:mm:ss,SSSx"),
-    ISO8601_OFFSET_DATE_TIME_HHMM(
-            "yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
-    ISO8601_OFFSET_DATE_TIME_HHCMM(
-            "yyyy-MM-dd'T'HH:mm:ss,SSSyyyy-MM-dd'T'HH:mm:ss,SSSXXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
+    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
+    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSXXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
     ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS", "yyyy-MM-dd'T'HH:mm:ss.SSS"),
     ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.nnnnnn", "yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
     US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS", "dd/MM/yy HH:mm:ss.SSS"),

From 1966a311c57af5cdf3173e287454be0f6ac6c136 Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Thu, 3 Jul 2025 16:03:09 +0300
Subject: [PATCH 06/34] fixes some of @vy comments

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../core/pattern/DatePatternConverter.java    | 40 +-------
 .../log4j/core/pattern/NamedPattern.java      | 98 +++++++++++++------
 .../log4j/core/pattern/package-info.java      |  2 +-
 3 files changed, 71 insertions(+), 69 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index 88f4588ab0e..0a3fb0bf8b6 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -63,7 +63,7 @@ private static InstantFormatter createFormatter(@Nullable final String[] options
             logOptionReadFailure(options, error, "failed for options: {}, falling back to the default instance");
         }
         return InstantPatternFormatter.newBuilder()
-                .setPattern(NamedPattern.DEFAULT.getNonLegacyPattern())
+                .setPattern(NamedPattern.DEFAULT.getPattern())
                 .build();
     }
 
@@ -94,7 +94,7 @@ private static InstantFormatter createFormatterUnsafely(@Nullable final String[]
     private static String readPattern(@Nullable final String[] options) {
         return options != null && options.length > 0 && options[0] != null
                 ? decodeNamedPattern(options[0])
-                : NamedPattern.DEFAULT.getNonLegacyPattern();
+                : NamedPattern.DEFAULT.getPattern();
     }
 
     /**
@@ -109,42 +109,8 @@ private static String readPattern(@Nullable final String[] options) {
      * @since 2.25.0
      */
     static String decodeNamedPattern(final String pattern) {
-
-        // If legacy formatters are enabled, we need to produce output aimed for `FixedDateFormat` and `FastDateFormat`.
-        // Otherwise, we need to produce output aimed for `DateTimeFormatter`.
-        // In conclusion, we need to check if legacy formatters enabled and apply following transformations.
-        //
-        //                               | Microseconds | Nanoseconds | Time-zone
-        // ------------------------------+--------------+-------------+-----------
-        // Legacy formatter directive    | nnnnnn       | nnnnnnnnn   | X, XX, XXX
-        // `DateTimeFormatter` directive | SSSSSS       | SSSSSSSSS   | x, xx, xxx
-        //
-        // Enabling legacy formatters mean that user requests the pattern to be formatted using deprecated
-        // `FixedDateFormat` and `FastDateFormat`.
-        // These two have, let's not say _bogus_, but an _interesting_ way of handling certain pattern directives:
-        //
-        // - They say they adhere to `SimpleDateFormat` specification, but use `n` directive.
-        //   `n` is neither defined by `SimpleDateFormat`, nor `SimpleDateFormat` supports sub-millisecond precisions.
-        //   `n` is probably manually introduced by Log4j to support sub-millisecond precisions.
-        //
-        // - `n` denotes nano-of-second for `DateTimeFormatter`.
-        //   In Java 17, `n` and `N` (nano-of-day) always output nanosecond precision.
-        //   This is independent of how many times they occur consequently.
-        //   Yet legacy formatters use repeated `n` to denote sub-milliseconds precision of certain length.
-        //   This doesn't work for `DateTimeFormatter`, which needs
-        //
-        //   - `SSSSSS` for 6-digit microsecond precision
-        //   - `SSSSSSSSS` for 9-digit nanosecond precision
-        //
-        // - Legacy formatters use `X`, `XX,` and `XXX` to choose between `+00`, `+0000`, or `+00:00`.
-        //   This is the correct behaviour for `SimpleDateFormat`.
-        //   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
-        //   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
         try {
-            final NamedPattern namedPattern = NamedPattern.valueOf(pattern);
-            return InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED
-                    ? namedPattern.getLegacyPattern()
-                    : namedPattern.getNonLegacyPattern();
+            return NamedPattern.valueOf(pattern).getPattern();
         } catch (IllegalArgumentException ignored) { // for Java 22+ it can be changed to `IllegalArgumentException _`
             return pattern;
         }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
index cef77decfb8..78343d52668 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
@@ -16,41 +16,77 @@
  */
 package org.apache.logging.log4j.core.pattern;
 
+import org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter;
+
+// If legacy formatters are enabled, we need to produce output aimed for `FixedDateFormat` and `FastDateFormat`.
+// Otherwise, we need to produce output aimed for `DateTimeFormatter`.
+// In conclusion, we need to check if legacy formatters enabled and apply following transformations.
+//
+//                               | Microseconds | Nanoseconds | Time-zone
+// ------------------------------+--------------+-------------+-----------
+// Legacy formatter directive    | nnnnnn       | nnnnnnnnn   | X, XX, XXX
+// `DateTimeFormatter` directive | SSSSSS       | SSSSSSSSS   | x, xx, xxx
+//
+// Enabling legacy formatters mean that user requests the pattern to be formatted using deprecated
+// `FixedDateFormat` and `FastDateFormat`.
+// These two have, let's not say _bogus_, but an _interesting_ way of handling certain pattern directives:
+//
+// - They say they adhere to `SimpleDateFormat` specification, but use `n` directive.
+//   `n` is neither defined by `SimpleDateFormat`, nor `SimpleDateFormat` supports sub-millisecond precisions.
+//   `n` is probably manually introduced by Log4j to support sub-millisecond precisions.
+//
+// - `n` denotes nano-of-second for `DateTimeFormatter`.
+//   In Java 17, `n` and `N` (nano-of-day) always output nanosecond precision.
+//   This is independent of how many times they occur consequently.
+//   Yet legacy formatters use repeated `n` to denote sub-milliseconds precision of certain length.
+//   This doesn't work for `DateTimeFormatter`, which needs
+//
+//   - `SSSSSS` for 6-digit microsecond precision
+//   - `SSSSSSSSS` for 9-digit nanosecond precision
+//
+// - Legacy formatters use `X`, `XX,` and `XXX` to choose between `+00`, `+0000`, or `+00:00`.
+//   This is the correct behaviour for `SimpleDateFormat`.
+//   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
+//   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
+/**
+ * Represents named date/time patterns for formatting log timestamps.
+ * Provides patterns for legacy and modern formatters based on configuration.
+ */
 @SuppressWarnings("SpellCheckingInspection")
 public enum NamedPattern {
-    ABSOLUTE("HH:mm:ss,SSS", "HH:mm:ss,SSS"),
-    ABSOLUTE_MICROS("HH:mm:ss,nnnnnn", "HH:mm:ss,SSSSSS"),
-    ABSOLUTE_NANOS("HH:mm:ss,nnnnnnnnn", "HH:mm:ss,SSSSSSSSS"),
-    ABSOLUTE_PERIOD("HH:mm:ss.SSS", "HH:mm:ss.SSS"),
-    COMPACT("yyyyMMddHHmmssSSS", "yyyyMMddHHmmssSSS"),
-    DATE("dd MMM yyyy HH:mm:ss,SSS", "dd MMM yyyy HH:mm:ss,SSS"),
-    DATE_PERIOD("dd MMM yyyy HH:mm:ss.SSS", "dd MMM yyyy HH:mm:ss.SSS"),
-    DEFAULT("yyyy-MM-dd HH:mm:ss,SSS", "yyyy-MM-dd HH:mm:ss,SSS"),
-    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,nnnnnn", "yyyy-MM-dd HH:mm:ss,SSSSSS"),
-    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,nnnnnnnnn", "yyyy-MM-dd HH:mm:ss,SSSSSSSSS"),
-    DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS", "yyyy-MM-dd HH:mm:ss.SSS"),
-    ISO8601_BASIC("yyyyMMdd'T'HHmmss,SSS", "yyyyMMdd'T'HHmmss,SSS"),
-    ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS", "yyyyMMdd'T'HHmmss.SSS"),
-    ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS", "yyyy-MM-dd'T'HH:mm:ss,SSS"),
-    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSX", "yyyy-MM-dd'T'HH:mm:ss,SSSx"),
-    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
-    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSXXX", "yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
-    ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS", "yyyy-MM-dd'T'HH:mm:ss.SSS"),
-    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.nnnnnn", "yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
-    US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS", "dd/MM/yy HH:mm:ss.SSS"),
-    US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS", "dd/MM/yyyy HH:mm:ss.SSS");
-    private final String legacyPattern, nonLegacyPattern;
-
-    NamedPattern(String legacyPattern, String nonLegacyPattern) {
-        this.legacyPattern = legacyPattern;
-        this.nonLegacyPattern = nonLegacyPattern;
-    }
+    ABSOLUTE("HH:mm:ss,SSS"),
+    ABSOLUTE_MICROS("HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
+    ABSOLUTE_NANOS("HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
+    ABSOLUTE_PERIOD("HH:mm:ss.SSS"),
+    COMPACT("yyyyMMddHHmmssSSS"),
+    DATE("dd MMM yyyy HH:mm:ss,SSS"),
+    DATE_PERIOD("dd MMM yyyy HH:mm:ss.SSS"),
+    DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
+    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
+    DEFAULT_NANOS(
+            "yyyy-MM-dd HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
+    DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS"),
+    ISO8601_BASIC("yyyyMMdd'T'HHmmss,SSS"),
+    ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS"),
+    ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
+    ISO8601_OFFSET_DATE_TIME_HH(
+            "yyyy-MM-dd'T'HH:mm:ss,SSS" + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "X" : "x")),
+    ISO8601_OFFSET_DATE_TIME_HHMM(
+            "yyyy-MM-dd'T'HH:mm:ss,SSS" + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "XX" : "xx")),
+    ISO8601_OFFSET_DATE_TIME_HHCMM(
+            "yyyy-MM-dd'T'HH:mm:ss,SSS" + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "XXX" : "xxx")),
+    ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS"),
+    ISO8601_PERIOD_MICROS(
+            "yyyy-MM-dd'T'HH:mm:ss." + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
+    US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS"),
+    US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
+    private final String pattern;
 
-    public String getLegacyPattern() {
-        return legacyPattern;
+    NamedPattern(String pattern) {
+        this.pattern = pattern;
     }
 
-    public String getNonLegacyPattern() {
-        return nonLegacyPattern;
+    public String getPattern() {
+        return pattern;
     }
 }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/package-info.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/package-info.java
index ac6407f47b3..df5bc576a25 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/package-info.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/package-info.java
@@ -18,7 +18,7 @@
  * Provides classes implementing format specifiers in conversion patterns.
  */
 @Export
-@Version("2.24.1")
+@Version("2.26.0")
 package org.apache.logging.log4j.core.pattern;
 
 import org.osgi.annotation.bundle.Export;

From 3418e4c0ebebe3e1a20e93dbcadf24e92fcfc916 Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Thu, 3 Jul 2025 17:56:37 +0300
Subject: [PATCH 07/34] changed enum to `NamedDatePattern`

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../logging/log4j/core/pattern/DatePatternConverter.java    | 6 +++---
 .../pattern/{NamedPattern.java => NamedDatePattern.java}    | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)
 rename log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/{NamedPattern.java => NamedDatePattern.java} (98%)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index 0a3fb0bf8b6..90c1f589b19 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -63,7 +63,7 @@ private static InstantFormatter createFormatter(@Nullable final String[] options
             logOptionReadFailure(options, error, "failed for options: {}, falling back to the default instance");
         }
         return InstantPatternFormatter.newBuilder()
-                .setPattern(NamedPattern.DEFAULT.getPattern())
+                .setPattern(NamedDatePattern.DEFAULT.getPattern())
                 .build();
     }
 
@@ -94,7 +94,7 @@ private static InstantFormatter createFormatterUnsafely(@Nullable final String[]
     private static String readPattern(@Nullable final String[] options) {
         return options != null && options.length > 0 && options[0] != null
                 ? decodeNamedPattern(options[0])
-                : NamedPattern.DEFAULT.getPattern();
+                : NamedDatePattern.DEFAULT.getPattern();
     }
 
     /**
@@ -110,7 +110,7 @@ private static String readPattern(@Nullable final String[] options) {
      */
     static String decodeNamedPattern(final String pattern) {
         try {
-            return NamedPattern.valueOf(pattern).getPattern();
+            return NamedDatePattern.valueOf(pattern).getPattern();
         } catch (IllegalArgumentException ignored) { // for Java 22+ it can be changed to `IllegalArgumentException _`
             return pattern;
         }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
similarity index 98%
rename from log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
rename to log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
index 78343d52668..2eb87170e2a 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
@@ -53,7 +53,7 @@
  * Provides patterns for legacy and modern formatters based on configuration.
  */
 @SuppressWarnings("SpellCheckingInspection")
-public enum NamedPattern {
+public enum NamedDatePattern {
     ABSOLUTE("HH:mm:ss,SSS"),
     ABSOLUTE_MICROS("HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
     ABSOLUTE_NANOS("HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
@@ -82,7 +82,7 @@ public enum NamedPattern {
     US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
     private final String pattern;
 
-    NamedPattern(String pattern) {
+    NamedDatePattern(String pattern) {
         this.pattern = pattern;
     }
 

From 975841394d77e97ba378e8d7e6e50169e52ac109 Mon Sep 17 00:00:00 2001
From: Roy Ash <roy.ash456@gmail.com>
Date: Fri, 4 Jul 2025 11:30:31 +0300
Subject: [PATCH 08/34] now taking all named patterns automatically

Signed-off-by: Roy Ash <roy.ash456@gmail.com>
---
 .../pattern/DatePatternConverterTestBase.java | 26 +++----------------
 1 file changed, 3 insertions(+), 23 deletions(-)

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java
index 99bd9c706de..a01457ed6e4 100644
--- a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java
@@ -26,6 +26,7 @@
 import java.util.Calendar;
 import java.util.Date;
 import java.util.TimeZone;
+import java.util.stream.Stream;
 import org.apache.logging.log4j.core.AbstractLogEvent;
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.time.Instant;
@@ -329,29 +330,8 @@ void testNewInstanceAllowsNullParameter() {
         DatePatternConverter.newInstance(null); // no errors
     }
 
-    private static final String[] PATTERN_NAMES = {
-        "ABSOLUTE",
-        "ABSOLUTE_MICROS",
-        "ABSOLUTE_NANOS",
-        "ABSOLUTE_PERIOD",
-        "COMPACT",
-        "DATE",
-        "DATE_PERIOD",
-        "DEFAULT",
-        "DEFAULT_MICROS",
-        "DEFAULT_NANOS",
-        "DEFAULT_PERIOD",
-        "ISO8601_BASIC",
-        "ISO8601_BASIC_PERIOD",
-        "ISO8601",
-        "ISO8601_OFFSET_DATE_TIME_HH",
-        "ISO8601_OFFSET_DATE_TIME_HHMM",
-        "ISO8601_OFFSET_DATE_TIME_HHCMM",
-        "ISO8601_PERIOD",
-        "ISO8601_PERIOD_MICROS",
-        "US_MONTH_DAY_YEAR2_TIME",
-        "US_MONTH_DAY_YEAR4_TIME"
-    };
+    private static final String[] PATTERN_NAMES =
+            Stream.of(NamedDatePattern.values()).map(Enum::name).toArray(String[]::new);
 
     @Test
     void testPredefinedFormatWithoutTimezone() {

From 0ef914b2a18c48675979c20094a8ceb9a1b5a579 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Volkan=20Yaz=C4=B1c=C4=B1?= <volkan.yazici@oracle.com>
Date: Tue, 8 Jul 2025 10:24:12 +0200
Subject: [PATCH 09/34] Improve style and cross references in docs

---
 .../core/pattern/DatePatternConverter.java    |   2 +-
 .../log4j/core/pattern/NamedDatePattern.java  | 114 +++++++++++-------
 ...ported_named_patterns_into_public_enum.xml |   5 +-
 3 files changed, 72 insertions(+), 49 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index 90c1f589b19..44d6f403fb6 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -111,7 +111,7 @@ private static String readPattern(@Nullable final String[] options) {
     static String decodeNamedPattern(final String pattern) {
         try {
             return NamedDatePattern.valueOf(pattern).getPattern();
-        } catch (IllegalArgumentException ignored) { // for Java 22+ it can be changed to `IllegalArgumentException _`
+        } catch (IllegalArgumentException ignored) {
             return pattern;
         }
     }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
index 2eb87170e2a..6425f6b5621 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
@@ -16,70 +16,92 @@
  */
 package org.apache.logging.log4j.core.pattern;
 
+import static org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED;
+
 import org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter;
 
-// If legacy formatters are enabled, we need to produce output aimed for `FixedDateFormat` and `FastDateFormat`.
-// Otherwise, we need to produce output aimed for `DateTimeFormatter`.
-// In conclusion, we need to check if legacy formatters enabled and apply following transformations.
-//
-//                               | Microseconds | Nanoseconds | Time-zone
-// ------------------------------+--------------+-------------+-----------
-// Legacy formatter directive    | nnnnnn       | nnnnnnnnn   | X, XX, XXX
-// `DateTimeFormatter` directive | SSSSSS       | SSSSSSSSS   | x, xx, xxx
-//
-// Enabling legacy formatters mean that user requests the pattern to be formatted using deprecated
-// `FixedDateFormat` and `FastDateFormat`.
-// These two have, let's not say _bogus_, but an _interesting_ way of handling certain pattern directives:
-//
-// - They say they adhere to `SimpleDateFormat` specification, but use `n` directive.
-//   `n` is neither defined by `SimpleDateFormat`, nor `SimpleDateFormat` supports sub-millisecond precisions.
-//   `n` is probably manually introduced by Log4j to support sub-millisecond precisions.
-//
-// - `n` denotes nano-of-second for `DateTimeFormatter`.
-//   In Java 17, `n` and `N` (nano-of-day) always output nanosecond precision.
-//   This is independent of how many times they occur consequently.
-//   Yet legacy formatters use repeated `n` to denote sub-milliseconds precision of certain length.
-//   This doesn't work for `DateTimeFormatter`, which needs
-//
-//   - `SSSSSS` for 6-digit microsecond precision
-//   - `SSSSSSSSS` for 9-digit nanosecond precision
-//
-// - Legacy formatters use `X`, `XX,` and `XXX` to choose between `+00`, `+0000`, or `+00:00`.
-//   This is the correct behaviour for `SimpleDateFormat`.
-//   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
-//   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
 /**
- * Represents named date/time patterns for formatting log timestamps.
- * Provides patterns for legacy and modern formatters based on configuration.
+ * Represents named date & time patterns for formatting log timestamps.
+ *
+ * @see InstantPatternFormatter#LEGACY_FORMATTERS_ENABLED
+ * @see DatePatternConverter
+ * @since 2.26.0
  */
-@SuppressWarnings("SpellCheckingInspection")
 public enum NamedDatePattern {
+
+    // If legacy formatters are enabled, we need to produce output aimed for `FixedDateFormat` and `FastDateFormat`.
+    // Otherwise, we need to produce output aimed for `DateTimeFormatter`.
+    // In conclusion, we need to check if legacy formatters enabled and apply following transformations.
+    //
+    //                               | Microseconds | Nanoseconds | Time-zone
+    // ------------------------------+--------------+-------------+-----------
+    // Legacy formatter directive    | nnnnnn       | nnnnnnnnn   | X, XX, XXX
+    // `DateTimeFormatter` directive | SSSSSS       | SSSSSSSSS   | x, xx, xxx
+    //
+    // Enabling legacy formatters mean that user requests the pattern to be formatted using deprecated
+    // `FixedDateFormat` and `FastDateFormat`.
+    // These two have, let's not say _bogus_, but an _interesting_ way of handling certain pattern directives:
+    //
+    // - They say they adhere to `SimpleDateFormat` specification, but use `n` directive.
+    //   `n` is neither defined by `SimpleDateFormat`, nor `SimpleDateFormat` supports sub-millisecond precisions.
+    //   `n` is probably manually introduced by Log4j to support sub-millisecond precisions.
+    //
+    // - `n` denotes nano-of-second for `DateTimeFormatter`.
+    //   In Java 17, `n` and `N` (nano-of-day) always output nanosecond precision.
+    //   This is independent of how many times they occur consequently.
+    //   Yet legacy formatters use repeated `n` to denote sub-milliseconds precision of certain length.
+    //   This doesn't work for `DateTimeFormatter`, which needs
+    //
+    //   - `SSSSSS` for 6-digit microsecond precision
+    //   - `SSSSSSSSS` for 9-digit nanosecond precision
+    //
+    // - Legacy formatters use `X`, `XX,` and `XXX` to choose between `+00`, `+0000`, or `+00:00`.
+    //   This is the correct behaviour for `SimpleDateFormat`.
+    //   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
+    //   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
+
     ABSOLUTE("HH:mm:ss,SSS"),
-    ABSOLUTE_MICROS("HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
-    ABSOLUTE_NANOS("HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
+
+    ABSOLUTE_MICROS("HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
+
+    ABSOLUTE_NANOS("HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
+
     ABSOLUTE_PERIOD("HH:mm:ss.SSS"),
+
     COMPACT("yyyyMMddHHmmssSSS"),
+
     DATE("dd MMM yyyy HH:mm:ss,SSS"),
+
     DATE_PERIOD("dd MMM yyyy HH:mm:ss.SSS"),
+
     DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
-    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
-    DEFAULT_NANOS(
-            "yyyy-MM-dd HH:mm:ss," + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
+
+    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
+
+    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
+
     DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS"),
+
     ISO8601_BASIC("yyyyMMdd'T'HHmmss,SSS"),
+
     ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS"),
+
     ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
-    ISO8601_OFFSET_DATE_TIME_HH(
-            "yyyy-MM-dd'T'HH:mm:ss,SSS" + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "X" : "x")),
-    ISO8601_OFFSET_DATE_TIME_HHMM(
-            "yyyy-MM-dd'T'HH:mm:ss,SSS" + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "XX" : "xx")),
-    ISO8601_OFFSET_DATE_TIME_HHCMM(
-            "yyyy-MM-dd'T'HH:mm:ss,SSS" + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "XXX" : "xxx")),
+
+    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSS" + (LEGACY_FORMATTERS_ENABLED ? "X" : "x")),
+
+    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSS" + (LEGACY_FORMATTERS_ENABLED ? "XX" : "xx")),
+
+    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSS" + (LEGACY_FORMATTERS_ENABLED ? "XXX" : "xxx")),
+
     ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS"),
-    ISO8601_PERIOD_MICROS(
-            "yyyy-MM-dd'T'HH:mm:ss." + (InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
+
+    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss." + (LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
+
     US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS"),
+
     US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
+
     private final String pattern;
 
     NamedDatePattern(String pattern) {
diff --git a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
index 377bf063178..eaad2b2d133 100644
--- a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
+++ b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
@@ -2,6 +2,7 @@
 <entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="https://logging.apache.org/xml/ns"
        xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="changed">
-  <description format="asciidoc">Exported named-patterns into its own public enum</description>
+       type="added">
+  <issue id="3789" link="https://github.com/apache/logging-log4j2/pull/3789"/>
+  <description format="asciidoc">Add and export `org.apache.logging.log4j.core.pattern.NamedDatePattern` class where users can programmatically access named date & time patterns supported by Pattern Layout</description>
 </entry>

From 1f4916a0022a481708784cba59403a0bcddf7edc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Volkan=20Yaz=C4=B1c=C4=B1?= <volkan.yazici@oracle.com>
Date: Tue, 8 Jul 2025 10:25:34 +0200
Subject: [PATCH 10/34] Fix XML typo

---
 .../.2.x.x/exported_named_patterns_into_public_enum.xml         | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
index eaad2b2d133..90d5205e4e6 100644
--- a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
+++ b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
@@ -4,5 +4,5 @@
        xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
        type="added">
   <issue id="3789" link="https://github.com/apache/logging-log4j2/pull/3789"/>
-  <description format="asciidoc">Add and export `org.apache.logging.log4j.core.pattern.NamedDatePattern` class where users can programmatically access named date & time patterns supported by Pattern Layout</description>
+  <description format="asciidoc">Add and export `org.apache.logging.log4j.core.pattern.NamedDatePattern` class where users can programmatically access named date &amp; time patterns supported by Pattern Layout</description>
 </entry>

From 4ce71a1bbd5acfc68e4d957bcbddf700dcb9050f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Volkan=20Yaz=C4=B1c=C4=B1?= <volkan@yazi.ci>
Date: Tue, 8 Jul 2025 10:26:30 +0200
Subject: [PATCH 11/34] Improve changelog description

---
 .../.2.x.x/exported_named_patterns_into_public_enum.xml         | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
index 90d5205e4e6..06a6efb335e 100644
--- a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
+++ b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
@@ -4,5 +4,5 @@
        xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
        type="added">
   <issue id="3789" link="https://github.com/apache/logging-log4j2/pull/3789"/>
-  <description format="asciidoc">Add and export `org.apache.logging.log4j.core.pattern.NamedDatePattern` class where users can programmatically access named date &amp; time patterns supported by Pattern Layout</description>
+  <description format="asciidoc">Add and export `org.apache.logging.log4j.core.pattern.NamedDatePattern` enabling users to programmatically access named date &amp; time patterns supported by Pattern Layout</description>
 </entry>

From 2c51fdd73b4b89ba1236bdfae20c97cf71fcf021 Mon Sep 17 00:00:00 2001
From: Johan Compagner <jcompagner@gmail.com>
Date: Mon, 30 Jun 2025 18:57:18 +0200
Subject: [PATCH 12/34] introduced a jakarta support range for the bnd tool
 (#3791)

Fixes #3787
---
 log4j-jakarta-web/pom.xml                           |  3 +++
 ...rta-web_relax_the_import_package_constraints.xml | 13 +++++++++++++
 2 files changed, 16 insertions(+)
 create mode 100644 src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml

diff --git a/log4j-jakarta-web/pom.xml b/log4j-jakarta-web/pom.xml
index 9dc66676119..4c5f33a4db8 100644
--- a/log4j-jakarta-web/pom.xml
+++ b/log4j-jakarta-web/pom.xml
@@ -39,6 +39,9 @@
       -->
     <bnd-module-name>org.apache.logging.log4j.web</bnd-module-name>
     <Fragment-Host>org.apache.logging.log4j.core</Fragment-Host>
+    <jakarta.support.range>[5.0,7)</jakarta.support.range>
+    <bnd-extra-package-options>jakarta.servlet;version="${jakarta.support.range}",
+      jakarta.servlet.http;version="${jakarta.support.range}"</bnd-extra-package-options>
   </properties>
 
   <dependencies>
diff --git a/src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml b/src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml
new file mode 100644
index 00000000000..9602fb8af87
--- /dev/null
+++ b/src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="changed">
+    <issue id="3787" link="https://github.com/apache/logging-log4j2/issues/3787"/>
+    <description format="asciidoc">
+     add a bnd tool property that makes sure that the supported jakarta version has a wider range then 5 to 6
+     Support the current release version for 5 to 7
+    </description>
+</entry>

From b1c0f4ecb2ccd5ab89003df21884a0584d7ba17b Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Thu, 3 Jul 2025 16:02:29 +0200
Subject: [PATCH 13/34] doc: Clarify and enhance `GraalVmProcessor`
 configuration example (#3786)

This update refines the `GraalVmProcessor` configuration example in response to feedback from #3755. The goal is to make the example more reliable and aligned with common Maven project setups. Key improvements include:

* **Ensuring consistent parameter usage:**
  The example now adds `-Alog4j.graalvm.groupId` and `-Alog4j.graalvm.artifactId` to **all executions** of the Maven Compiler Plugin. This guarantees correct behavior regardless of the execution ID used in user projects.

* **Simplifying plugin execution setup:**
  Instead of introducing a dedicated `generate-log4j-plugin-descriptor` execution, the example now modifies the existing `default-compile` execution. This reflects the most typical use case, where annotation processing and compilation occur together.

These changes aim to make the setup easier to adopt while reducing configuration errors.
---
 .../modules/ROOT/pages/manual/plugins.adoc    | 29 ++++++++++---------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/src/site/antora/modules/ROOT/pages/manual/plugins.adoc b/src/site/antora/modules/ROOT/pages/manual/plugins.adoc
index 233b6fd3226..6b751f07366 100644
--- a/src/site/antora/modules/ROOT/pages/manual/plugins.adoc
+++ b/src/site/antora/modules/ROOT/pages/manual/plugins.adoc
@@ -211,8 +211,8 @@ annotation processor creates such a file at compile-time.
 
 [WARNING]
 ====
-The `GraalVmProcessor` needs to know the `groupId` and `artifactId` coordinates of your project.
-These must be supplied to the processor using the `log4j.graalvm.groupId` and `log4j.graalvm.artifactId` annotation processor options.
+The `GraalVmProcessor` requires your project's `groupId` and `artifactId` to correctly generate the GraalVM reachability metadata file in the recommended location.
+Provide these values to the processor using the `log4j.graalvm.groupId` and `log4j.graalvm.artifactId` annotation processor options.
 ====
 
 You need to configure your build tool as follows to use both plugin processors:
@@ -227,15 +227,23 @@ Maven::
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-compiler-plugin</artifactId>
   <version>${maven-compiler-plugin.version}</version>
+  <configuration>
+    <compilerArgs>
+        <!-- Provide the project coordinates to `GraalVmProcessor`: -->
+        <arg>-Alog4j.graalvm.groupId=${project.groupId}</arg>
+        <arg>-Alog4j.graalvm.artifactId=${project.artifactId}</arg>
+    </compilerArgs>
+  </configuration>
   <executions>
     <execution>
-      <id>generate-log4j-plugin-descriptor</id>
-      <goals>
-        <goal>compile</goal>
-      </goals>
-      <phase>process-classes</phase>
+        <!--
+          ~ Explicitly list the annotation processors for the default compile execution.
+          ~ This is required starting with JDK 23, where annotation processors are not enabled automatically.
+          ~ Explicit configuration also improves build reliability and clarity.
+          ~ For more details, see: https://inside.java/2024/06/18/quality-heads-up/
+          -->
+      <id>default-compile</id>
       <configuration>
-        <proc>only</proc>
         <annotationProcessorPaths>
           <!-- Include `log4j-core` providing
                1. `org.apache.logging.log4j.core.config.plugins.processor.PluginProcessor` that generates `Log4j2Plugins.dat`
@@ -252,11 +260,6 @@ Maven::
           <!-- Process sources using `GraalVmProcessor` to generate a GraalVM reachability metadata file -->
           <processor>org.apache.logging.log4j.core.config.plugins.processor.GraalVmProcessor</processor>
         </annotationProcessors>
-        <compilerArgs>
-          <!-- Provide the project coordinates to `GraalVmProcessor`: -->
-          <arg>-Alog4j.graalvm.groupId=${project.groupId}</arg>
-          <arg>-Alog4j.graalvm.artifactId=${project.artifactId}</arg>
-        </compilerArgs>
       </configuration>
     </execution>
   </executions>

From 087751507504ad0affb93e460ee7409b717853d5 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Thu, 3 Jul 2025 16:55:32 +0200
Subject: [PATCH 14/34] fix: Fix Java type for annotated array parameters
 (#3797)

This update fixes the GraalVM reachability metadata generation for methods with annotated array parameters, such as `@Nullable String[]`.

Previously, the code computed the fully qualified class name for the parameter using the **raw** type, which retained the annotations (e.g., `@org.jspecify.annotations.Nullable java.lang.String`). This resulted in incorrect metadata that was ignored by GraalVM.

The issue is resolved by transforming the `DeclaredType` into a `TypeElement`, effectively removing any annotations, and then calling `getQualifiedName()` to correctly generate the fully qualified class name without annotations.
---
 .../processor/GraalVmProcessorTest.java       | 24 ++++++++--
 .../java/FakeConverter.java                   | 46 +++++++++++++++++++
 .../plugins/processor/GraalVmProcessor.java   |  4 +-
 .../3796_annotated-array-parameters.xml       | 12 +++++
 4 files changed, 81 insertions(+), 5 deletions(-)
 create mode 100644 log4j-core-test/src/test/resources/GraalVmProcessorTest/java/FakeConverter.java
 create mode 100644 src/changelog/.2.x.x/3796_annotated-array-parameters.xml

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessorTest.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessorTest.java
index 9bdbcad8dd9..957bb3228cd 100644
--- a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessorTest.java
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessorTest.java
@@ -103,6 +103,18 @@ class GraalVmProcessorTest {
     private static final Object FAKE_CONSTRAINT_VALIDATOR = onlyNoArgsConstructor(FAKE_CONSTRAINT_VALIDATOR_NAME);
     private static final String FAKE_PLUGIN_VISITOR_NAME = "example.FakeAnnotations$FakePluginVisitor";
     private static final Object FAKE_PLUGIN_VISITOR = onlyNoArgsConstructor(FAKE_PLUGIN_VISITOR_NAME);
+    private static final String FAKE_CONVERTER_NAME = "example.FakeConverter";
+    private static final Object FAKE_CONVERTER = asMap(
+            "name",
+            FAKE_CONVERTER_NAME,
+            "methods",
+            singletonList(asMap(
+                    "name",
+                    "newInstance",
+                    "parameterTypes",
+                    asList("org.apache.logging.log4j.core.config.Configuration", "java.lang.String[]"))),
+            "fields",
+            emptyList());
 
     private static final String GROUP_ID = "groupId";
     private static final String ARTIFACT_ID = "artifactId";
@@ -155,7 +167,8 @@ static Stream<Arguments> containsSpecificEntries() {
                 Arguments.of(FAKE_PLUGIN_BUILDER_NAME, FAKE_PLUGIN_BUILDER),
                 Arguments.of(FAKE_PLUGIN_NESTED_NAME, FAKE_PLUGIN_NESTED),
                 Arguments.of(FAKE_CONSTRAINT_VALIDATOR_NAME, FAKE_CONSTRAINT_VALIDATOR),
-                Arguments.of(FAKE_PLUGIN_VISITOR_NAME, FAKE_PLUGIN_VISITOR));
+                Arguments.of(FAKE_PLUGIN_VISITOR_NAME, FAKE_PLUGIN_VISITOR),
+                Arguments.of(FAKE_CONVERTER_NAME, FAKE_CONVERTER));
     }
 
     @ParameterizedTest
@@ -168,7 +181,9 @@ void containsSpecificEntries(String className, Object expectedJson) throws IOExc
         assertThatJson(reachabilityMetadata)
                 .inPath(String.format("$[?(@.name == '%s')]", className))
                 .isArray()
-                .contains(json(expectedJson));
+                .hasSize(1)
+                .first()
+                .isEqualTo(json(expectedJson));
     }
 
     static Stream<Arguments> reachabilityMetadataPath() {
@@ -214,7 +229,7 @@ void whenNoGroupIdAndArtifactId_thenWarningIsPrinted(@TempDir(cleanup = CleanupM
         }
         // The generated folder name should be deterministic and based solely on the descriptor content.
         // If the descriptor changes, this test and the expected folder name must be updated accordingly.
-        assertThat(reachabilityMetadataFolders).hasSize(1).containsExactly(path.resolve("62162090"));
+        assertThat(reachabilityMetadataFolders).hasSize(1).containsExactly(path.resolve("72c240aa"));
         assertThat(reachabilityMetadataFolders.get(0).resolve("reflect-config.json"))
                 .as("Reachability metadata file")
                 .exists();
@@ -250,7 +265,6 @@ private static List<String> generateDescriptor(
         }
 
         // Compile the sources
-        final Path descriptorFilePath = outputDir.resolve("plugins.xml");
         final DiagnosticCollector<JavaFileObject> diagnosticCollector = new DiagnosticCollector<>();
         final JavaCompiler.CompilationTask task =
                 compiler.getTask(null, fileManager, diagnosticCollector, options, null, sources);
@@ -260,6 +274,8 @@ private static List<String> generateDescriptor(
         return diagnosticCollector.getDiagnostics().stream()
                 .filter(d -> d.getKind() != Diagnostic.Kind.NOTE)
                 .map(d -> d.getMessage(Locale.ROOT))
+                // This message appears when the test runs on JDK 8
+                .filter(m -> !"unknown enum constant java.lang.annotation.ElementType.MODULE".equals(m))
                 .collect(Collectors.toList());
     }
 }
diff --git a/log4j-core-test/src/test/resources/GraalVmProcessorTest/java/FakeConverter.java b/log4j-core-test/src/test/resources/GraalVmProcessorTest/java/FakeConverter.java
new file mode 100644
index 00000000000..0b15cb4ecc1
--- /dev/null
+++ b/log4j-core-test/src/test/resources/GraalVmProcessorTest/java/FakeConverter.java
@@ -0,0 +1,46 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package example;
+
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.pattern.ConverterKeys;
+import org.apache.logging.log4j.core.pattern.LogEventPatternConverter;
+import org.apache.logging.log4j.core.pattern.PatternConverter;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+@NullMarked
+@Plugin(name = "FakePatternConverter", category = PatternConverter.CATEGORY)
+@ConverterKeys({"f", "fake"})
+public final class FakeConverter extends LogEventPatternConverter {
+
+    private FakeConverter(@Nullable final Configuration config, @Nullable final String[] options) {
+        super("Fake", "fake");
+    }
+
+    public static FakeConverter newInstance(
+            @Nullable final Configuration config, @Nullable final String[] options) {
+        return new FakeConverter(config, options);
+    }
+
+    @Override
+    public void format(LogEvent event, StringBuilder toAppendTo) {
+        toAppendTo.append("FakeConverter: ").append(event.getMessage().getFormattedMessage());
+    }
+}
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessor.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessor.java
index e6178f2a17e..a5ba7ba61c5 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessor.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/config/plugins/processor/GraalVmProcessor.java
@@ -300,7 +300,9 @@ public String visitArray(final ArrayType t, @Nullable Void unused) {
 
                     @Override
                     public @Nullable String visitDeclared(final DeclaredType t, final Void unused) {
-                        return processingEnv.getTypeUtils().erasure(t).toString();
+                        return safeCast(t.asElement(), TypeElement.class)
+                                .getQualifiedName()
+                                .toString();
                     }
                 },
                 null);
diff --git a/src/changelog/.2.x.x/3796_annotated-array-parameters.xml b/src/changelog/.2.x.x/3796_annotated-array-parameters.xml
new file mode 100644
index 00000000000..5be57fe6418
--- /dev/null
+++ b/src/changelog/.2.x.x/3796_annotated-array-parameters.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+    <issue id="3796" link="https://github.com/apache/logging-log4j2/issues/3796"/>
+    <description format="asciidoc">
+        Fix GraalVM reachability metadata generation for methods with annotated array type parameters, such as `@Nullable String[]`.
+    </description>
+</entry>

From 46a5fe2d70db0494b25ef2cc1e9a372e8889a73e Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 3 Jul 2025 22:49:21 +0200
Subject: [PATCH 15/34] Bump com.fasterxml.jackson:jackson-bom from 2.19.0 to
 2.19.1 in /log4j-parent (#3745)

* Update `com.fasterxml.jackson:jackson-bom` to version `2.19.1` (#3745)

* Empty commit to trigger required checks

---------

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Piotr P. Karwasz <pkarwasz-github@apache.org>
---
 log4j-parent/pom.xml | 2 +-
 pom.xml              | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/log4j-parent/pom.xml b/log4j-parent/pom.xml
index f4e56806a27..4bfd9f733af 100644
--- a/log4j-parent/pom.xml
+++ b/log4j-parent/pom.xml
@@ -88,7 +88,7 @@
     <hamcrest.version>3.0</hamcrest.version>
     <HdrHistogram.version>2.2.2</HdrHistogram.version>
     <hsqldb.version>2.7.4</hsqldb.version>
-    <jackson-bom.version>2.19.0</jackson-bom.version>
+    <jackson-bom.version>2.19.1</jackson-bom.version>
     <!-- Override the version in Jakarta EE 9 BOM: -->
     <jakarta-activation.version>2.1.3</jakarta-activation.version>
     <jakarta-mail.version>2.1.3</jakarta-mail.version>
diff --git a/pom.xml b/pom.xml
index a6be2bd0295..f10bb2f171f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -345,7 +345,7 @@
     <site-conversant.version>1.2.21</site-conversant.version>
     <site-disruptor.version>4.0.0</site-disruptor.version>
     <site-flume.version>1.11.0</site-flume.version>
-    <site-jackson.version>2.19.0</site-jackson.version>
+    <site-jackson.version>2.19.1</site-jackson.version>
     <site-javax-mail.version>1.6.2</site-javax-mail.version>
     <site-jctools.version>4.0.5</site-jctools.version>
     <site-je.version>18.3.12</site-je.version>

From 8afe8925d8467a206d099cddcfe50dec8c079a59 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 3 Jul 2025 21:11:10 +0000
Subject: [PATCH 16/34] Update `org.junit:junit-bom` to version `5.13.2`
 (#3782)

Co-authored-by: ASF Logging Services RM <private@logging.apache.org>
---
 log4j-parent/pom.xml                                | 2 +-
 src/changelog/.2.x.x/update_org_junit_junit_bom.xml | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 src/changelog/.2.x.x/update_org_junit_junit_bom.xml

diff --git a/log4j-parent/pom.xml b/log4j-parent/pom.xml
index 4bfd9f733af..d3ad93980cf 100644
--- a/log4j-parent/pom.xml
+++ b/log4j-parent/pom.xml
@@ -111,7 +111,7 @@
     <jmh.version>1.37</jmh.version>
     <jspecify.version>1.0.0</jspecify.version>
     <junit.version>4.13.2</junit.version>
-    <junit-jupiter.version>5.13.1</junit-jupiter.version>
+    <junit-jupiter.version>5.13.2</junit-jupiter.version>
     <junit-pioneer.version>1.9.1</junit-pioneer.version>
     <kafka.version>3.9.1</kafka.version>
     <lightcouch.version>0.2.0</lightcouch.version>
diff --git a/src/changelog/.2.x.x/update_org_junit_junit_bom.xml b/src/changelog/.2.x.x/update_org_junit_junit_bom.xml
new file mode 100644
index 00000000000..5c572a50a46
--- /dev/null
+++ b/src/changelog/.2.x.x/update_org_junit_junit_bom.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="updated">
+  <issue id="3782" link="https://github.com/apache/logging-log4j2/pull/3782"/>
+  <description format="asciidoc">Update `org.junit:junit-bom` to version `5.13.2`</description>
+</entry>

From 7f2fbe3aa7e6267ef73c728c8ae65a15b3438d1d Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Thu, 3 Jul 2025 21:11:24 +0000
Subject: [PATCH 17/34] Update `com.github.luben:zstd-jni` to version `1.5.7-4`
 (#3799)

Co-authored-by: ASF Logging Services RM <private@logging.apache.org>
---
 log4j-parent/pom.xml                                      | 2 +-
 src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml

diff --git a/log4j-parent/pom.xml b/log4j-parent/pom.xml
index d3ad93980cf..7da1ce0fafe 100644
--- a/log4j-parent/pom.xml
+++ b/log4j-parent/pom.xml
@@ -141,7 +141,7 @@
     <wiremock.version>2.35.2</wiremock.version>
     <xmlunit.version>2.10.3</xmlunit.version>
     <xz.version>1.10</xz.version>
-    <zstd.version>1.5.7-3</zstd.version>
+    <zstd.version>1.5.7-4</zstd.version>
 
     <!-- =====================================================
          Pinned transitive dependency version properties (in alphabetical order)
diff --git a/src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml b/src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml
new file mode 100644
index 00000000000..979784e1e2d
--- /dev/null
+++ b/src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="updated">
+  <issue id="3799" link="https://github.com/apache/logging-log4j2/pull/3799"/>
+  <description format="asciidoc">Update `com.github.luben:zstd-jni` to version `1.5.7-4`</description>
+</entry>

From 8b889ba8da0450db8febfa534bb49e5969ed23b3 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Fri, 4 Jul 2025 14:29:06 +0200
Subject: [PATCH 18/34] fix: Disable sharing of formatted timestamps between
 threads (#3802)

This change disables the sharing of formatted timestamps between threads in `InstantPatternThreadLocalCachedFormatter`.

Previously, a mutable `StringBuilder` was shared across threads via a cached object. This could lead to situations where one thread ("owner") was modifying the builder while another thread was reading from it, resulting in inaccurate or truncated timestamps.

This fix ensures that only thread-local instances are used, preventing concurrency issues and improving timestamp correctness under load.

This change is similar in nature to #1485 and fixes #3792.
---
 ...PatternThreadLocalCachedFormatterTest.java | 54 +++++++++++++++++++
 ...tantPatternThreadLocalCachedFormatter.java | 31 ++++-------
 .../3792_formatted-datetime-sharing.xml       | 13 +++++
 3 files changed, 76 insertions(+), 22 deletions(-)
 create mode 100644 src/changelog/.2.x.x/3792_formatted-datetime-sharing.xml

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatterTest.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatterTest.java
index 1f94b0b9aef..f4435c0086d 100644
--- a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatterTest.java
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatterTest.java
@@ -16,12 +16,14 @@
  */
 package org.apache.logging.log4j.core.util.internal.instant;
 
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.when;
@@ -30,6 +32,8 @@
 import java.util.Locale;
 import java.util.Random;
 import java.util.TimeZone;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
 import java.util.function.Function;
 import org.apache.logging.log4j.core.time.Instant;
 import org.apache.logging.log4j.core.time.MutableInstant;
@@ -37,6 +41,7 @@
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import org.junit.jupiter.params.provider.ValueSource;
+import org.junitpioneer.jupiter.Issue;
 
 class InstantPatternThreadLocalCachedFormatterTest {
 
@@ -289,4 +294,53 @@ private static MutableInstant createInstant(final long epochMillis, final int ep
         instant.initFromEpochMilli(epochMillis, epochMillisNanos);
         return instant;
     }
+
+    @Test
+    @Issue("https://github.com/apache/logging-log4j2/issues/3792")
+    void should_be_thread_safe() throws Exception {
+        // Instead of randomly testing the thread safety, we test that the current implementation does not
+        // cache results across threads.
+        //
+        // Modify this test if the implementation changes in the future.
+        final InstantPatternFormatter patternFormatter = mock(InstantPatternFormatter.class);
+        when(patternFormatter.getPrecision()).thenReturn(ChronoUnit.MILLIS);
+
+        final Instant instant = INSTANT0;
+        final String output = "thread-output";
+        doAnswer(invocation -> {
+                    StringBuilder buffer = invocation.getArgument(0);
+                    buffer.append(output)
+                            .append('-')
+                            .append(Thread.currentThread().getName());
+                    return null;
+                })
+                .when(patternFormatter)
+                .formatTo(any(StringBuilder.class), eq(instant));
+
+        final InstantFormatter cachedFormatter =
+                InstantPatternThreadLocalCachedFormatter.ofMilliPrecision(patternFormatter);
+
+        final int threadCount = 2;
+        for (int i = 0; i < threadCount; i++) {
+            formatOnNewThread(cachedFormatter, instant, output);
+        }
+        verify(patternFormatter, times(threadCount)).formatTo(any(StringBuilder.class), eq(instant));
+    }
+
+    private static void formatOnNewThread(
+            final InstantFormatter formatter, final Instant instant, final String expectedOutput)
+            throws ExecutionException, InterruptedException {
+        ExecutorService executor = newSingleThreadExecutor();
+        try {
+            executor.submit(() -> {
+                        String formatted = formatter.format(instant);
+                        assertThat(formatted)
+                                .isEqualTo(expectedOutput + "-"
+                                        + Thread.currentThread().getName());
+                    })
+                    .get();
+        } finally {
+            executor.shutdown();
+        }
+    }
 }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatter.java
index 96bf4504aa3..c5179382ff9 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternThreadLocalCachedFormatter.java
@@ -38,8 +38,6 @@ final class InstantPatternThreadLocalCachedFormatter implements InstantPatternFo
     private final ThreadLocal<Object[]> epochInstantAndBufferRef =
             ThreadLocal.withInitial(InstantPatternThreadLocalCachedFormatter::createEpochInstantAndBuffer);
 
-    private Object[] lastEpochInstantAndBuffer = createEpochInstantAndBuffer();
-
     private static Object[] createEpochInstantAndBuffer() {
         return new Object[] {-1L, new StringBuilder()};
     }
@@ -89,32 +87,21 @@ public ChronoUnit getPrecision() {
     public void formatTo(final StringBuilder buffer, final Instant instant) {
         requireNonNull(buffer, "buffer");
         requireNonNull(instant, "instant");
-        final Object[] prevEpochInstantAndBuffer = lastEpochInstantAndBuffer;
-        final long prevEpochInstant = (long) prevEpochInstantAndBuffer[0];
-        final StringBuilder prevBuffer = (StringBuilder) prevEpochInstantAndBuffer[1];
+        final Object[] epochInstantAndBuffer = epochInstantAndBufferRef.get();
+        final long prevEpochInstant = (long) epochInstantAndBuffer[0];
+        final StringBuilder localBuffer = (StringBuilder) epochInstantAndBuffer[1];
         final long nextEpochInstant = epochInstantExtractor.apply(instant);
-        if (prevEpochInstant == nextEpochInstant) {
-            buffer.append(prevBuffer);
-        } else {
-
-            // We could have used `StringBuilders.trimToMaxSize()` on `prevBuffer`.
+        if (prevEpochInstant != nextEpochInstant) {
+            // We could have used `StringBuilders.trimToMaxSize()` on `localBuffer`.
             // That is, we wouldn't want exploded `StringBuilder`s in hundreds of `ThreadLocal`s.
             // Though we are formatting instants and always expect to produce strings of more or less the same length.
             // Hence, no need for truncation.
 
-            // Populate a new cache entry
-            final Object[] nextEpochInstantAndBuffer = epochInstantAndBufferRef.get();
-            nextEpochInstantAndBuffer[0] = nextEpochInstant;
-            final StringBuilder nextBuffer = (StringBuilder) nextEpochInstantAndBuffer[1];
-            nextBuffer.setLength(0);
-            formatter.formatTo(nextBuffer, instant);
-
-            // Update the effective cache entry
-            lastEpochInstantAndBuffer = nextEpochInstantAndBuffer;
-
-            // Help out the request
-            buffer.append(nextBuffer);
+            epochInstantAndBuffer[0] = nextEpochInstant;
+            localBuffer.setLength(0);
+            formatter.formatTo(localBuffer, instant);
         }
+        buffer.append(localBuffer);
     }
 
     @Override
diff --git a/src/changelog/.2.x.x/3792_formatted-datetime-sharing.xml b/src/changelog/.2.x.x/3792_formatted-datetime-sharing.xml
new file mode 100644
index 00000000000..ad52ea95387
--- /dev/null
+++ b/src/changelog/.2.x.x/3792_formatted-datetime-sharing.xml
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- SPDX-License-Identifier: Apache-2.0 -->
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3792" link="https://github.com/apache/logging-log4j2/issues/3792"/>
+  <description format="asciidoc">
+    Fix timestamp formatting concurrency issue, when `log4j2.enabledThreadlocals` is `true`.
+  </description>
+</entry>

From b408f815974b3bcf29e92296441f9eba4f478330 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Fri, 4 Jul 2025 18:43:08 +0200
Subject: [PATCH 19/34] fix: Add GraalVM reachability metadata for non-plugin
 class instantiations (#3800)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The `GraalVmProcessor` currently only generates metadata for Log4j plugins, overlooking other reflection usages in Log4j Core. This change adds reachability metadata for additional reflection cases to improve compatibility with GraalVM native images.

### Fixed Cases

This PR addresses the following reflective instantiations:

* **Context selectors and reliability strategies:** Ensures proper instantiation under GraalVM.
* **`Configuration` instantiation in `DefaultConfigurationBuilder`:** Fixes support for the `log4j2.properties` configuration format when running on GraalVM.
* **`BlockingQueue` instantiation in JSON Template Layout:** Enables GraalVM compatibility. Note: `MpmcArrayQueue` is not supported on GraalVM and must be fixed in the JCTools project.

### Known Limitations (Explicitly Ignored)

The following cases are *not* addressed in this PR:

* **JMX classes in `log4j-1.2-api`:** While GraalVM supports JMX, usage of Log4j 1.x’s JMX interface is likely minimal.
* **`MulticastDnsAdvertiser`:** This feature is probably unused and could pose a security risk by advertising log file locations via mDNS.
---
 .../log4j-api/resource-config.json            |   2 +-
 .../log4j-core/reflect-config.json            | 120 ++++++++++++++++++
 .../log4j-core/resource-config.json           |   2 +-
 .../reflect-config.json                       |  24 ++++
 .../resource-config.json                      |   1 +
 .../.2.x.x/3800_graalvm-misc-reflection.xml   |  12 ++
 6 files changed, 159 insertions(+), 2 deletions(-)
 create mode 100644 log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/reflect-config.json
 create mode 100644 log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/reflect-config.json
 create mode 100644 src/changelog/.2.x.x/3800_graalvm-misc-reflection.xml

diff --git a/log4j-api/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-api/resource-config.json b/log4j-api/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-api/resource-config.json
index 1649e6be1ef..9b4eb75dc63 100644
--- a/log4j-api/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-api/resource-config.json
+++ b/log4j-api/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-api/resource-config.json
@@ -6,4 +6,4 @@
       }
     ]
   }
-}
\ No newline at end of file
+}
diff --git a/log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/reflect-config.json b/log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/reflect-config.json
new file mode 100644
index 00000000000..5411a855b98
--- /dev/null
+++ b/log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/reflect-config.json
@@ -0,0 +1,120 @@
+[
+  {
+    "name": "org.apache.logging.log4j.core.config.builder.impl.BuiltConfiguration",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": [
+          "org.apache.logging.log4j.core.LoggerContext",
+          "org.apache.logging.log4j.core.config.ConfigurationSource",
+          "org.apache.logging.log4j.core.config.builder.api.Component"
+        ]
+      }
+    ],
+    "fields": []
+  },
+  {
+    "name": "org.apache.logging.log4j.core.config.properties.PropertiesConfiguration",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": [
+          "org.apache.logging.log4j.core.LoggerContext",
+          "org.apache.logging.log4j.core.config.ConfigurationSource",
+          "org.apache.logging.log4j.core.config.builder.api.Component"
+        ]
+      }
+    ],
+    "fields": []
+  },
+  {
+    "name": "org.apache.logging.log4j.core.async.BasicAsyncLoggerContextSelector",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.selector.BasicContextSelector",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.selector.JndiContextSelector",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.selector.ClassLoaderContextSelector",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.async.AsyncLoggerContextSelector",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.osgi.BundleContextSelector",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.config.LockingReliabilityStrategy",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.config.AwaitUnconditionallyReliabilityStrategy",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.config.DefaultReliabilityStrategy",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  },
+  {
+    "name": "org.apache.logging.log4j.core.config.AwaitCompletionReliabilityStrategy",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": []
+      }
+    ]
+  }
+]
diff --git a/log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/resource-config.json b/log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/resource-config.json
index d5b51667ed9..9f1049ed8ba 100644
--- a/log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/resource-config.json
+++ b/log4j-core/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-core/resource-config.json
@@ -9,4 +9,4 @@
       }
     ]
   }
-}
\ No newline at end of file
+}
diff --git a/log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/reflect-config.json b/log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/reflect-config.json
new file mode 100644
index 00000000000..c4e3872cd69
--- /dev/null
+++ b/log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/reflect-config.json
@@ -0,0 +1,24 @@
+[
+  {
+    "name": "org.jctools.queues.MpmcArrayQueue",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": [
+          "int"
+        ]
+      }
+    ]
+  },
+  {
+    "name": "java.util.concurrent.ArrayBlockingQueue",
+    "methods": [
+      {
+        "name": "<init>",
+        "parameterTypes": [
+          "int"
+        ]
+      }
+    ]
+  }
+]
diff --git a/log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/resource-config.json b/log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/resource-config.json
index c8afe14794a..55c503ebebc 100644
--- a/log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/resource-config.json
+++ b/log4j-layout-template-json/src/main/resources/META-INF/native-image/org.apache.logging.log4j/log4j-layout-template-json/resource-config.json
@@ -7,3 +7,4 @@
     ]
   }
 }
+
diff --git a/src/changelog/.2.x.x/3800_graalvm-misc-reflection.xml b/src/changelog/.2.x.x/3800_graalvm-misc-reflection.xml
new file mode 100644
index 00000000000..3e6653c121f
--- /dev/null
+++ b/src/changelog/.2.x.x/3800_graalvm-misc-reflection.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3800" link="https://github.com/apache/logging-log4j2/pull/3800"/>
+  <description format="asciidoc">
+    Resolves `PropertiesConfiguration` compatibility issues with GraalVM and addresses additional minor reflection-related problems.
+  </description>
+</entry>

From ea6deb77d59757aca8e50804bc8b255970a04067 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Fri, 4 Jul 2025 20:33:11 +0200
Subject: [PATCH 20/34] fix: Add `resource:` protocol to allowed URL schemes by
 default (#3795)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* fix: Add `resource:` protocol to allowed URL schemes by default

This update includes `resource:` in the list of allowed URL schemes for retrieving configuration files.
See [`log4j2.configurationAllowedProtocols`](https://logging.apache.org/log4j/2.x/manual/systemproperties.html#log4j2.configurationAllowedProtocols)

Currently, the `resource:` protocol is used exclusively by a `URLStreamHandler` that retrieves files from the embedded resources in a GraalVM native image. This makes it a secure and appropriate source for trusted configuration files.

This change cannot be easily and reliably tested through a unit test. An integration test will be provided in apache/logging-log4j-samples#345

Closes #3790

* fix: Add `resource` protocol only in native images

This change introduces an internal `SystemUtils.isGraalVm()` method to detect the presence of GraalVM and enable the `resource` protocol.

* Reword changelog entry

---------

Co-authored-by: Volkan Yazıcı <volkan@yazi.ci>
---
 .../log4j/core/net/UrlConnectionFactory.java  | 20 ++++++++++++++++++-
 .../log4j/core/util/internal/SystemUtils.java | 16 +++++++++++++++
 .../.2.x.x/3790_allow-resource-protocol.xml   | 12 +++++++++++
 .../properties-transport-security.adoc        | 14 ++++++++++---
 4 files changed, 58 insertions(+), 4 deletions(-)
 create mode 100644 src/changelog/.2.x.x/3790_allow-resource-protocol.xml

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/net/UrlConnectionFactory.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/net/UrlConnectionFactory.java
index e6ba2a13665..e98d3d9a9db 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/net/UrlConnectionFactory.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/net/UrlConnectionFactory.java
@@ -33,6 +33,7 @@
 import org.apache.logging.log4j.core.net.ssl.SslConfiguration;
 import org.apache.logging.log4j.core.net.ssl.SslConfigurationFactory;
 import org.apache.logging.log4j.core.util.AuthorizationProvider;
+import org.apache.logging.log4j.core.util.internal.SystemUtils;
 import org.apache.logging.log4j.util.PropertiesUtil;
 import org.apache.logging.log4j.util.Strings;
 
@@ -51,7 +52,24 @@ public class UrlConnectionFactory {
     private static final String HTTP = "http";
     private static final String HTTPS = "https";
     private static final String JAR = "jar";
-    private static final String DEFAULT_ALLOWED_PROTOCOLS = "https, file, jar";
+    /**
+     * Default list of protocols that are allowed to be used for configuration files and other trusted resources.
+     * <p>
+     *     By default, we trust the following protocols:
+     * <dl>
+     *     <dt>file</dt>
+     *     <dd>Local files</dd>
+     *     <dt>https</dt>
+     *     <dd>Resources retrieved through TLS to guarantee their integrity</dd>
+     *     <dt>jar</dt>
+     *     <dd>Resources retrieved from JAR files</dd>
+     *     <dt>resource</dt>
+     *     <dd>Resources embedded in a GraalVM native image</dd>
+     * </dl>
+     */
+    private static final String DEFAULT_ALLOWED_PROTOCOLS =
+            SystemUtils.isGraalVm() ? "file, https, jar, resource" : "file, https, jar";
+
     private static final String NO_PROTOCOLS = "_none";
     public static final String ALLOWED_PROTOCOLS = "log4j2.Configuration.allowedProtocols";
 
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/SystemUtils.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/SystemUtils.java
index b7b3d9cbb4d..23d60ce688a 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/SystemUtils.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/SystemUtils.java
@@ -36,5 +36,21 @@ public static boolean isOsAndroid() {
         return getJavaVendor().contains("Android");
     }
 
+    /**
+     * Checks if the current runtime is GraalVM.
+     * <p>
+     *     See <a href="https://www.graalvm.org/sdk/javadoc/org/graalvm/nativeimage/ImageInfo.html#PROPERTY_IMAGE_CODE_KEY">ImageInfo.PROPERTY_IMAGE_CODE_KEY</a>.
+     * </p>
+     * @return true if the current runtime is GraalVM, false otherwise.
+     */
+    public static boolean isGraalVm() {
+        try {
+            return System.getProperty("org.graalvm.nativeimage.imagecode") != null;
+        } catch (final SecurityException e) {
+            LOGGER.debug("Unable to determine if the current runtime is GraalVM.", e);
+            return false;
+        }
+    }
+
     private SystemUtils() {}
 }
diff --git a/src/changelog/.2.x.x/3790_allow-resource-protocol.xml b/src/changelog/.2.x.x/3790_allow-resource-protocol.xml
new file mode 100644
index 00000000000..ffa3c80e305
--- /dev/null
+++ b/src/changelog/.2.x.x/3790_allow-resource-protocol.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3790" link="https://github.com/apache/logging-log4j2/issues/3790"/>
+  <description format="asciidoc">
+    Allow `resource:` protocol for configuration files by default, if the current runtime is GraalVM.
+  </description>
+</entry>
diff --git a/src/site/antora/modules/ROOT/partials/manual/systemproperties/properties-transport-security.adoc b/src/site/antora/modules/ROOT/partials/manual/systemproperties/properties-transport-security.adoc
index 445c9ec5418..3c662698c95 100644
--- a/src/site/antora/modules/ROOT/partials/manual/systemproperties/properties-transport-security.adoc
+++ b/src/site/antora/modules/ROOT/partials/manual/systemproperties/properties-transport-security.adoc
@@ -21,9 +21,17 @@
 
 [cols="1h,5"]
 |===
-| Env. variable | `LOG4J_CONFIGURATION_ALLOWED_PROTOCOLS`
-| Type          | Comma-separated list of https://docs.oracle.com/javase/{java-target-version}/docs/api/java/net/URL.html[`URL`] protocols
-| Default value | `file, https, jar`
+| Env. variable
+| `LOG4J_CONFIGURATION_ALLOWED_PROTOCOLS`
+
+| Type
+| Comma-separated list of https://docs.oracle.com/javase/{java-target-version}/docs/api/java/net/URL.html[`URL`] protocols
+
+| Default value
+|
+`file, https, jar` (JVM)
+
+`file, https, jar, resource` (GraalVM)
 |===
 
 A comma separated list of https://docs.oracle.com/javase/{java-target-version}/docs/api/java/net/URL.html[`URL`] protocols that may be used to load any kind of configuration source.

From d1e3cb53e2bd9d50cf659b050f6584fe568b8733 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Mon, 7 Jul 2025 14:59:03 +0200
Subject: [PATCH 21/34] Bump org.junit:junit-bom from 5.13.2 to 5.13.3 in
 /log4j-parent (#3806)

Bumps [org.junit:junit-bom](https://github.com/junit-team/junit-framework) from 5.13.2 to 5.13.3.
- [Release notes](https://github.com/junit-team/junit-framework/releases)
- [Commits](https://github.com/junit-team/junit-framework/compare/r5.13.2...r5.13.3)

---
updated-dependencies:
- dependency-name: org.junit:junit-bom
  dependency-version: 5.13.3
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 log4j-parent/pom.xml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/log4j-parent/pom.xml b/log4j-parent/pom.xml
index 7da1ce0fafe..8302fab4d2f 100644
--- a/log4j-parent/pom.xml
+++ b/log4j-parent/pom.xml
@@ -111,7 +111,7 @@
     <jmh.version>1.37</jmh.version>
     <jspecify.version>1.0.0</jspecify.version>
     <junit.version>4.13.2</junit.version>
-    <junit-jupiter.version>5.13.2</junit-jupiter.version>
+    <junit-jupiter.version>5.13.3</junit-jupiter.version>
     <junit-pioneer.version>1.9.1</junit-pioneer.version>
     <kafka.version>3.9.1</kafka.version>
     <lightcouch.version>0.2.0</lightcouch.version>

From 94e060d09a4d9b1cf411701a28cd4a42d002cb56 Mon Sep 17 00:00:00 2001
From: Roy <roy.ash456@gmail.com>
Date: Wed, 9 Jul 2025 11:17:44 +0300
Subject: [PATCH 22/34] Apply suggestion from @ppkarwasz

Co-authored-by: Piotr P. Karwasz <piotr@github.copernik.eu>
---
 .../org/apache/logging/log4j/core/pattern/NamedDatePattern.java | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
index 6425f6b5621..2d974e98d09 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
@@ -21,7 +21,7 @@
 import org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter;
 
 /**
- * Represents named date & time patterns for formatting log timestamps.
+ * Represents named date &amp; time patterns for formatting log timestamps.
  *
  * @see InstantPatternFormatter#LEGACY_FORMATTERS_ENABLED
  * @see DatePatternConverter

From 66c83825aa461b1086f817d58891613b41814af4 Mon Sep 17 00:00:00 2001
From: Roy <roy.ash456@gmail.com>
Date: Wed, 9 Jul 2025 12:41:14 +0000
Subject: [PATCH 23/34] implemented @ppkarwasz & @vy chamges regarding
 `FixedDateFormat.FixedFormat`

---
 .../pattern/DatePatternConverterTestBase.java |   2 +-
 .../core/pattern/DatePatternConverter.java    |  38 +++++-
 .../log4j/core/pattern/NamedDatePattern.java  | 114 ------------------
 .../core/pattern/NamedInstantPattern.java     |  78 ++++++++++++
 ...ported_named_patterns_into_public_enum.xml |   2 +-
 5 files changed, 115 insertions(+), 119 deletions(-)
 delete mode 100644 log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
 create mode 100644 log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java
index a01457ed6e4..16fd89ac30b 100644
--- a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/DatePatternConverterTestBase.java
@@ -331,7 +331,7 @@ void testNewInstanceAllowsNullParameter() {
     }
 
     private static final String[] PATTERN_NAMES =
-            Stream.of(NamedDatePattern.values()).map(Enum::name).toArray(String[]::new);
+            Stream.of(NamedInstantPattern.values()).map(Enum::name).toArray(String[]::new);
 
     @Test
     void testPredefinedFormatWithoutTimezone() {
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index 44d6f403fb6..7e173b33155 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -63,7 +63,7 @@ private static InstantFormatter createFormatter(@Nullable final String[] options
             logOptionReadFailure(options, error, "failed for options: {}, falling back to the default instance");
         }
         return InstantPatternFormatter.newBuilder()
-                .setPattern(NamedDatePattern.DEFAULT.getPattern())
+                .setPattern(NamedInstantPattern.DEFAULT.getPattern())
                 .build();
     }
 
@@ -94,7 +94,7 @@ private static InstantFormatter createFormatterUnsafely(@Nullable final String[]
     private static String readPattern(@Nullable final String[] options) {
         return options != null && options.length > 0 && options[0] != null
                 ? decodeNamedPattern(options[0])
-                : NamedDatePattern.DEFAULT.getPattern();
+                : NamedInstantPattern.DEFAULT.getPattern();
     }
 
     /**
@@ -109,8 +109,40 @@ private static String readPattern(@Nullable final String[] options) {
      * @since 2.25.0
      */
     static String decodeNamedPattern(final String pattern) {
+        // If legacy formatters are enabled, we need to produce output aimed for `FixedDateFormat` and `FastDateFormat`.
+        // Otherwise, we need to produce output aimed for `DateTimeFormatter`.
+        // In conclusion, we need to check if legacy formatters enabled and apply following transformations.
+        //
+        //                               | Microseconds | Nanoseconds | Time-zone
+        // ------------------------------+--------------+-------------+-----------
+        // Legacy formatter directive    | nnnnnn       | nnnnnnnnn   | X, XX, XXX
+        // `DateTimeFormatter` directive | SSSSSS       | SSSSSSSSS   | x, xx, xxx
+        //
+        // Enabling legacy formatters mean that user requests the pattern to be formatted using deprecated
+        // `FixedDateFormat` and `FastDateFormat`.
+        // These two have, let's not say _bogus_, but an _interesting_ way of handling certain pattern directives:
+        //
+        // - They say they adhere to `SimpleDateFormat` specification, but use `n` directive.
+        //   `n` is neither defined by `SimpleDateFormat`, nor `SimpleDateFormat` supports sub-millisecond precisions.
+        //   `n` is probably manually introduced by Log4j to support sub-millisecond precisions.
+        //
+        // - `n` denotes nano-of-second for `DateTimeFormatter`.
+        //   In Java 17, `n` and `N` (nano-of-day) always output nanosecond precision.
+        //   This is independent of how many times they occur consequently.
+        //   Yet legacy formatters use repeated `n` to denote sub-milliseconds precision of certain length.
+        //   This doesn't work for `DateTimeFormatter`, which needs
+        //
+        //   - `SSSSSS` for 6-digit microsecond precision
+        //   - `SSSSSSSSS` for 9-digit nanosecond precision
+        //
+        // - Legacy formatters use `X`, `XX,` and `XXX` to choose between `+00`, `+0000`, or `+00:00`.
+        //   This is the correct behaviour for `SimpleDateFormat`.
+        //   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
+        //   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
         try {
-            return NamedDatePattern.valueOf(pattern).getPattern();
+            return InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED
+                    ? FixedDateFormat.FixedFormat.valueOf(pattern).getPattern()
+                    : NamedInstantPattern.valueOf(pattern).getPattern();
         } catch (IllegalArgumentException ignored) {
             return pattern;
         }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
deleted file mode 100644
index 2d974e98d09..00000000000
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedDatePattern.java
+++ /dev/null
@@ -1,114 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to you under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.apache.logging.log4j.core.pattern;
-
-import static org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED;
-
-import org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter;
-
-/**
- * Represents named date &amp; time patterns for formatting log timestamps.
- *
- * @see InstantPatternFormatter#LEGACY_FORMATTERS_ENABLED
- * @see DatePatternConverter
- * @since 2.26.0
- */
-public enum NamedDatePattern {
-
-    // If legacy formatters are enabled, we need to produce output aimed for `FixedDateFormat` and `FastDateFormat`.
-    // Otherwise, we need to produce output aimed for `DateTimeFormatter`.
-    // In conclusion, we need to check if legacy formatters enabled and apply following transformations.
-    //
-    //                               | Microseconds | Nanoseconds | Time-zone
-    // ------------------------------+--------------+-------------+-----------
-    // Legacy formatter directive    | nnnnnn       | nnnnnnnnn   | X, XX, XXX
-    // `DateTimeFormatter` directive | SSSSSS       | SSSSSSSSS   | x, xx, xxx
-    //
-    // Enabling legacy formatters mean that user requests the pattern to be formatted using deprecated
-    // `FixedDateFormat` and `FastDateFormat`.
-    // These two have, let's not say _bogus_, but an _interesting_ way of handling certain pattern directives:
-    //
-    // - They say they adhere to `SimpleDateFormat` specification, but use `n` directive.
-    //   `n` is neither defined by `SimpleDateFormat`, nor `SimpleDateFormat` supports sub-millisecond precisions.
-    //   `n` is probably manually introduced by Log4j to support sub-millisecond precisions.
-    //
-    // - `n` denotes nano-of-second for `DateTimeFormatter`.
-    //   In Java 17, `n` and `N` (nano-of-day) always output nanosecond precision.
-    //   This is independent of how many times they occur consequently.
-    //   Yet legacy formatters use repeated `n` to denote sub-milliseconds precision of certain length.
-    //   This doesn't work for `DateTimeFormatter`, which needs
-    //
-    //   - `SSSSSS` for 6-digit microsecond precision
-    //   - `SSSSSSSSS` for 9-digit nanosecond precision
-    //
-    // - Legacy formatters use `X`, `XX,` and `XXX` to choose between `+00`, `+0000`, or `+00:00`.
-    //   This is the correct behaviour for `SimpleDateFormat`.
-    //   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
-    //   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
-
-    ABSOLUTE("HH:mm:ss,SSS"),
-
-    ABSOLUTE_MICROS("HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
-
-    ABSOLUTE_NANOS("HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
-
-    ABSOLUTE_PERIOD("HH:mm:ss.SSS"),
-
-    COMPACT("yyyyMMddHHmmssSSS"),
-
-    DATE("dd MMM yyyy HH:mm:ss,SSS"),
-
-    DATE_PERIOD("dd MMM yyyy HH:mm:ss.SSS"),
-
-    DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
-
-    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
-
-    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss," + (LEGACY_FORMATTERS_ENABLED ? "nnnnnnnnn" : "SSSSSSSSS")),
-
-    DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS"),
-
-    ISO8601_BASIC("yyyyMMdd'T'HHmmss,SSS"),
-
-    ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS"),
-
-    ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
-
-    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSS" + (LEGACY_FORMATTERS_ENABLED ? "X" : "x")),
-
-    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSS" + (LEGACY_FORMATTERS_ENABLED ? "XX" : "xx")),
-
-    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSS" + (LEGACY_FORMATTERS_ENABLED ? "XXX" : "xxx")),
-
-    ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS"),
-
-    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss." + (LEGACY_FORMATTERS_ENABLED ? "nnnnnn" : "SSSSSS")),
-
-    US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS"),
-
-    US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
-
-    private final String pattern;
-
-    NamedDatePattern(String pattern) {
-        this.pattern = pattern;
-    }
-
-    public String getPattern() {
-        return pattern;
-    }
-}
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
new file mode 100644
index 00000000000..1c3bd14b484
--- /dev/null
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
@@ -0,0 +1,78 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.logging.log4j.core.pattern;
+
+/**
+ * Represents named date &amp; time patterns for formatting log timestamps.
+ *
+ * @see DatePatternConverter
+ * @since 2.26.0
+ */
+public enum NamedInstantPattern {
+
+    ABSOLUTE("HH:mm:ss,SSS"),
+
+    ABSOLUTE_MICROS("HH:mm:ss,SSSSSS"),
+
+    ABSOLUTE_NANOS("HH:mm:ss,SSSSSSSSS"),
+
+    ABSOLUTE_PERIOD("HH:mm:ss.SSS"),
+
+    COMPACT("yyyyMMddHHmmssSSS"),
+
+    DATE("dd MMM yyyy HH:mm:ss,SSS"),
+
+    DATE_PERIOD("dd MMM yyyy HH:mm:ss.SSS"),
+
+    DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
+
+    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,SSSSSS"),
+
+    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,SSSSSSSSS"),
+
+    DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS"),
+
+    ISO8601_BASIC("yyyyMMdd'T'HHmmss,SSS"),
+
+    ISO8601_BASIC_PERIOD("yyyyMMdd'T'HHmmss.SSS"),
+
+    ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
+
+    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSx"),
+
+    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
+
+    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
+
+    ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS"),
+
+    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
+
+    US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS"),
+
+    US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
+
+    private final String pattern;
+
+    NamedInstantPattern(String pattern) {
+        this.pattern = pattern;
+    }
+
+    public String getPattern() {
+        return pattern;
+    }
+}
diff --git a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
index 06a6efb335e..20fd32265d6 100644
--- a/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
+++ b/src/changelog/.2.x.x/exported_named_patterns_into_public_enum.xml
@@ -4,5 +4,5 @@
        xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
        type="added">
   <issue id="3789" link="https://github.com/apache/logging-log4j2/pull/3789"/>
-  <description format="asciidoc">Add and export `org.apache.logging.log4j.core.pattern.NamedDatePattern` enabling users to programmatically access named date &amp; time patterns supported by Pattern Layout</description>
+  <description format="asciidoc">Add and export `org.apache.logging.log4j.core.pattern.NamedInstantPattern` enabling users to programmatically access named date &amp; time patterns supported by Pattern Layout</description>
 </entry>

From ee48520048aaca0bea44606f4cb661a86b91d053 Mon Sep 17 00:00:00 2001
From: Roy Ash <roya@getneema.com>
Date: Wed, 9 Jul 2025 16:25:44 +0300
Subject: [PATCH 24/34] Added a JavaDoc for `NamedInstantPattern#getPattern`

Signed-off-by: Roy Ash <roya@getneema.com>
---
 .../logging/log4j/core/pattern/NamedInstantPattern.java       | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
index 1c3bd14b484..d5b75c6c057 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
@@ -23,7 +23,6 @@
  * @since 2.26.0
  */
 public enum NamedInstantPattern {
-
     ABSOLUTE("HH:mm:ss,SSS"),
 
     ABSOLUTE_MICROS("HH:mm:ss,SSSSSS"),
@@ -72,6 +71,9 @@ public enum NamedInstantPattern {
         this.pattern = pattern;
     }
 
+    /**
+     * @return pattern that is compatible with {@link java.time.format.DateTimeFormatter}
+     */
     public String getPattern() {
         return pattern;
     }

From 8066ba6869e25e5d2c0abcdc892efad205316345 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Wed, 9 Jul 2025 21:21:07 +0200
Subject: [PATCH 25/34] fix: expose legacy `FixedFormat` patterns via
 `NamedInstantPattern`

To decouple `DatePatternConverter` from `FixedFormat`, legacy pattern values are now provided through the `NamedInstantPattern.getLegacyPattern` method.

These patterns are specific to `FixedDateFormat` and not intended for general use, so the method is kept package-private.
---
 .../core/pattern/NamedInstantPatternTest.java | 45 +++++++++++++++++++
 .../core/pattern/DatePatternConverter.java    | 41 +++++------------
 .../core/pattern/NamedInstantPattern.java     | 41 +++++++++++++----
 3 files changed, 87 insertions(+), 40 deletions(-)
 create mode 100644 log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
new file mode 100644
index 00000000000..bbe5e6e45eb
--- /dev/null
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
@@ -0,0 +1,45 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.logging.log4j.core.pattern;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.time.Instant;
+import org.apache.logging.log4j.core.time.MutableInstant;
+import org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+
+class NamedInstantPatternTest {
+
+    @ParameterizedTest
+    @EnumSource(NamedInstantPattern.class)
+    void compatibilityOfLegacyPattern(NamedInstantPattern namedPattern) {
+        InstantPatternFormatter legacyFormatter = InstantPatternFormatter.newBuilder()
+                .setPattern(namedPattern.getLegacyPattern())
+                .setLegacyFormattersEnabled(true)
+                .build();
+        InstantPatternFormatter formatter = InstantPatternFormatter.newBuilder()
+                .setPattern(namedPattern.getPattern())
+                .setLegacyFormattersEnabled(false)
+                .build();
+        Instant javaTimeInstant = Instant.now();
+        MutableInstant instant = new MutableInstant();
+        instant.initFromEpochSecond(javaTimeInstant.getEpochSecond(), javaTimeInstant.getNano());
+        assertThat(legacyFormatter.format(instant)).isEqualTo(formatter.format(instant));
+    }
+}
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index 7e173b33155..e8ec1088c9c 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -109,40 +109,19 @@ private static String readPattern(@Nullable final String[] options) {
      * @since 2.25.0
      */
     static String decodeNamedPattern(final String pattern) {
-        // If legacy formatters are enabled, we need to produce output aimed for `FixedDateFormat` and `FastDateFormat`.
-        // Otherwise, we need to produce output aimed for `DateTimeFormatter`.
-        // In conclusion, we need to check if legacy formatters enabled and apply following transformations.
+        // `FixedDateFormat` accepted two types of patterns:
+        //   - the names of `FixedFormat` enum constants (identical to `NamedInstantPattern` enum names),
+        //   - or custom pattern strings.
         //
-        //                               | Microseconds | Nanoseconds | Time-zone
-        // ------------------------------+--------------+-------------+-----------
-        // Legacy formatter directive    | nnnnnn       | nnnnnnnnn   | X, XX, XXX
-        // `DateTimeFormatter` directive | SSSSSS       | SSSSSSSSS   | x, xx, xxx
-        //
-        // Enabling legacy formatters mean that user requests the pattern to be formatted using deprecated
-        // `FixedDateFormat` and `FastDateFormat`.
-        // These two have, let's not say _bogus_, but an _interesting_ way of handling certain pattern directives:
-        //
-        // - They say they adhere to `SimpleDateFormat` specification, but use `n` directive.
-        //   `n` is neither defined by `SimpleDateFormat`, nor `SimpleDateFormat` supports sub-millisecond precisions.
-        //   `n` is probably manually introduced by Log4j to support sub-millisecond precisions.
-        //
-        // - `n` denotes nano-of-second for `DateTimeFormatter`.
-        //   In Java 17, `n` and `N` (nano-of-day) always output nanosecond precision.
-        //   This is independent of how many times they occur consequently.
-        //   Yet legacy formatters use repeated `n` to denote sub-milliseconds precision of certain length.
-        //   This doesn't work for `DateTimeFormatter`, which needs
-        //
-        //   - `SSSSSS` for 6-digit microsecond precision
-        //   - `SSSSSSSSS` for 9-digit nanosecond precision
-        //
-        // - Legacy formatters use `X`, `XX,` and `XXX` to choose between `+00`, `+0000`, or `+00:00`.
-        //   This is the correct behaviour for `SimpleDateFormat`.
-        //   Though `X` in `DateTimeFormatter` produces `Z` for zero-offset.
-        //   To avoid the `Z` output, one needs to use `x` with `DateTimeFormatter`.
+        // To determine the format's precision, we cannot return the legacy name directly;
+        // instead, we must return the equivalent `FixedDateFormat` pattern string.
+        // These patterns are only recognized by `FixedDateFormat` so we make them available only
+        // via the package-private `getLegacyPattern()` method.
         try {
+            NamedInstantPattern namedInstantPattern = NamedInstantPattern.valueOf(pattern);
             return InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED
-                    ? FixedDateFormat.FixedFormat.valueOf(pattern).getPattern()
-                    : NamedInstantPattern.valueOf(pattern).getPattern();
+                    ? namedInstantPattern.getLegacyPattern()
+                    : namedInstantPattern.getPattern();
         } catch (IllegalArgumentException ignored) {
             return pattern;
         }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
index d5b75c6c057..a95a0ceda0b 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
@@ -16,18 +16,21 @@
  */
 package org.apache.logging.log4j.core.pattern;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * Represents named date &amp; time patterns for formatting log timestamps.
  *
  * @see DatePatternConverter
  * @since 2.26.0
  */
+@NullMarked
 public enum NamedInstantPattern {
     ABSOLUTE("HH:mm:ss,SSS"),
 
-    ABSOLUTE_MICROS("HH:mm:ss,SSSSSS"),
+    ABSOLUTE_MICROS("HH:mm:ss,SSSSSS", "HH:mm:ss,nnnnnn"),
 
-    ABSOLUTE_NANOS("HH:mm:ss,SSSSSSSSS"),
+    ABSOLUTE_NANOS("HH:mm:ss,SSSSSSSSS", "HH:mm:ss,nnnnnnnnn"),
 
     ABSOLUTE_PERIOD("HH:mm:ss.SSS"),
 
@@ -39,9 +42,9 @@ public enum NamedInstantPattern {
 
     DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
 
-    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,SSSSSS"),
+    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,SSSSSS", "yyyy-MM-dd HH:mm:ss,nnnnnn"),
 
-    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,SSSSSSSSS"),
+    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,SSSSSSSSS", "yyyy-MM-dd HH:mm:ss,nnnnnnnnn"),
 
     DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS"),
 
@@ -51,30 +54,50 @@ public enum NamedInstantPattern {
 
     ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
 
-    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSx"),
+    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSx", "yyyy-MM-dd'T'HH:mm:ss,SSSX"),
 
-    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
+    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSxx", "yyyy-MM-dd'T'HH:mm:ss,SSSXX"),
 
-    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
+    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSxxx", "yyyy-MM-dd'T'HH:mm:ss,SSSXXX"),
 
     ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS"),
 
-    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
+    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.SSSSSS", "yyyy-MM-dd'T'HH:mm:ss.nnnnnn"),
 
     US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS"),
 
     US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
 
     private final String pattern;
+    private final String legacyPattern;
 
     NamedInstantPattern(String pattern) {
+        this(pattern, pattern);
+    }
+
+    NamedInstantPattern(String pattern, String legacyPattern) {
         this.pattern = pattern;
+        this.legacyPattern = legacyPattern;
     }
 
     /**
-     * @return pattern that is compatible with {@link java.time.format.DateTimeFormatter}
+     * Returns the date-time pattern string compatible with {@link java.time.format.DateTimeFormatter}
+     * that is associated with this named pattern.
+     *
+     * @return the date-time pattern string for use with {@code DateTimeFormatter}
      */
     public String getPattern() {
         return pattern;
     }
+
+    /**
+     * Returns the legacy {@link org.apache.logging.log4j.core.util.datetime.FixedDateFormat} pattern
+     * associated with this named pattern.
+     *
+     * @return the legacy pattern string as used in
+     * {@link org.apache.logging.log4j.core.util.datetime.FixedDateFormat.FixedFormat}
+     */
+    String getLegacyPattern() {
+        return legacyPattern;
+    }
 }

From 6c7ed23cdeb0ce424cc96b0efc0b0fed501838e2 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Thu, 10 Jul 2025 10:00:20 +0200
Subject: [PATCH 26/34] fix: precision of `InstantPatternLegacyFormatter`

To get the correct precision in the `InstantPatternLegacyFormatter` we need to replace the legacy `n` pattern letter with its `DateTimeFormatter` equivalent `S`.
---
 .../logging/log4j/core/pattern/NamedInstantPatternTest.java  | 1 +
 .../util/internal/instant/InstantPatternLegacyFormatter.java | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
index bbe5e6e45eb..3754aa1bb53 100644
--- a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
@@ -41,5 +41,6 @@ void compatibilityOfLegacyPattern(NamedInstantPattern namedPattern) {
         MutableInstant instant = new MutableInstant();
         instant.initFromEpochSecond(javaTimeInstant.getEpochSecond(), javaTimeInstant.getNano());
         assertThat(legacyFormatter.format(instant)).isEqualTo(formatter.format(instant));
+        assertThat(legacyFormatter.getPrecision()).isEqualTo(formatter.getPrecision());
     }
 }
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java
index aaf380c7f0a..9d57493e5d6 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java
@@ -46,7 +46,10 @@ final class InstantPatternLegacyFormatter implements InstantPatternFormatter {
     private final BiConsumer<StringBuilder, Instant> formatter;
 
     InstantPatternLegacyFormatter(final String pattern, final Locale locale, final TimeZone timeZone) {
-        this.precision = new InstantPatternDynamicFormatter(pattern, locale, timeZone).getPrecision();
+        // Replaces 'n' used in legacy patterns with 'S' to obtain the right precision.
+        // In legacy patterns, the precision of 'n' depends on the pattern length, but
+        // in `DateTimeFormatter`, it is always nanoseconds.
+        this.precision = new InstantPatternDynamicFormatter(pattern.replace('n', 'S'), locale, timeZone).getPrecision();
         this.pattern = pattern;
         this.locale = locale;
         this.timeZone = timeZone;

From 7d77e1fdb3e283361cc871fef32e036e3ee3009e Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Thu, 10 Jul 2025 10:03:41 +0200
Subject: [PATCH 27/34] fix: dynamically compute legacy date format pattern

This change:

* Restores detailed documentation explaining the differences between `FixedDateFormat` and `DateTimeFormatter` patterns.
* Implements dynamic computation of the legacy pattern based on the documented rules, ensuring consistent behavior and improved maintainability.
---
 .../core/pattern/DatePatternConverter.java    | 10 +--
 .../core/pattern/NamedInstantPattern.java     | 88 ++++++++++++++++---
 2 files changed, 76 insertions(+), 22 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
index e8ec1088c9c..8b598c3de85 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/DatePatternConverter.java
@@ -109,14 +109,8 @@ private static String readPattern(@Nullable final String[] options) {
      * @since 2.25.0
      */
     static String decodeNamedPattern(final String pattern) {
-        // `FixedDateFormat` accepted two types of patterns:
-        //   - the names of `FixedFormat` enum constants (identical to `NamedInstantPattern` enum names),
-        //   - or custom pattern strings.
-        //
-        // To determine the format's precision, we cannot return the legacy name directly;
-        // instead, we must return the equivalent `FixedDateFormat` pattern string.
-        // These patterns are only recognized by `FixedDateFormat` so we make them available only
-        // via the package-private `getLegacyPattern()` method.
+        // See `NamedInstantPattern.getLegacyPattern()`
+        // for the difference between legacy and `DateTimeFormatter` patterns.
         try {
             NamedInstantPattern namedInstantPattern = NamedInstantPattern.valueOf(pattern);
             return InstantPatternFormatter.LEGACY_FORMATTERS_ENABLED
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
index a95a0ceda0b..449e95a456d 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
@@ -16,6 +16,7 @@
  */
 package org.apache.logging.log4j.core.pattern;
 
+import java.util.regex.Pattern;
 import org.jspecify.annotations.NullMarked;
 
 /**
@@ -28,9 +29,9 @@
 public enum NamedInstantPattern {
     ABSOLUTE("HH:mm:ss,SSS"),
 
-    ABSOLUTE_MICROS("HH:mm:ss,SSSSSS", "HH:mm:ss,nnnnnn"),
+    ABSOLUTE_MICROS("HH:mm:ss,SSSSSS"),
 
-    ABSOLUTE_NANOS("HH:mm:ss,SSSSSSSSS", "HH:mm:ss,nnnnnnnnn"),
+    ABSOLUTE_NANOS("HH:mm:ss,SSSSSSSSS"),
 
     ABSOLUTE_PERIOD("HH:mm:ss.SSS"),
 
@@ -42,9 +43,9 @@ public enum NamedInstantPattern {
 
     DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
 
-    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,SSSSSS", "yyyy-MM-dd HH:mm:ss,nnnnnn"),
+    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,SSSSSS"),
 
-    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,SSSSSSSSS", "yyyy-MM-dd HH:mm:ss,nnnnnnnnn"),
+    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,SSSSSSSSS"),
 
     DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS"),
 
@@ -54,30 +55,26 @@ public enum NamedInstantPattern {
 
     ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
 
-    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSx", "yyyy-MM-dd'T'HH:mm:ss,SSSX"),
+    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSx"),
 
-    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSxx", "yyyy-MM-dd'T'HH:mm:ss,SSSXX"),
+    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
 
-    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSxxx", "yyyy-MM-dd'T'HH:mm:ss,SSSXXX"),
+    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
 
     ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS"),
 
-    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.SSSSSS", "yyyy-MM-dd'T'HH:mm:ss.nnnnnn"),
+    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
 
     US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS"),
 
     US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
 
+    private static final Pattern NANO_PATTERN = Pattern.compile("S{4,}");
+
     private final String pattern;
-    private final String legacyPattern;
 
     NamedInstantPattern(String pattern) {
-        this(pattern, pattern);
-    }
-
-    NamedInstantPattern(String pattern, String legacyPattern) {
         this.pattern = pattern;
-        this.legacyPattern = legacyPattern;
     }
 
     /**
@@ -93,11 +90,74 @@ public String getPattern() {
     /**
      * Returns the legacy {@link org.apache.logging.log4j.core.util.datetime.FixedDateFormat} pattern
      * associated with this named pattern.
+     * <p>
+     * If legacy formatters are enabled, output is produced for
+     * {@code FixedDateFormat} and {@code FastDateFormat}. To convert the {@code DateTimeFormatter}
+     * to its legacy counterpart, the following transformations need to be applied:
+     * </p>
+     * <table>
+     *   <caption>Pattern Differences</caption>
+     *   <thead>
+     *     <tr>
+     *       <th></th>
+     *       <th>Microseconds</th>
+     *       <th>Nanoseconds</th>
+     *       <th>Time-zone</th>
+     *     </tr>
+     *   </thead>
+     *   <tbody>
+     *     <tr>
+     *       <td>Legacy formatter directive</td>
+     *       <td><code>nnnnnn</code></td>
+     *       <td><code>nnnnnnnnn</code></td>
+     *       <td><code>X</code>, <code>XX</code>, <code>XXX</code></td>
+     *     </tr>
+     *     <tr>
+     *       <td>{@code DateTimeFormatter} directive</td>
+     *       <td><code>SSSSSS</code></td>
+     *       <td><code>SSSSSSSSS</code></td>
+     *       <td><code>x</code>, <code>xx</code>, <code>xxx</code></td>
+     *     </tr>
+     *   </tbody>
+     * </table>
+     * <h2></h2>
+     * <ul>
+     *   <li>
+     *     <p>
+     *       Legacy formatters are largely compatible with the {@code SimpleDateFormat} specification,
+     *       but introduce a custom {@code n} pattern letter, unique to Log4j, to represent sub-millisecond precision.
+     *       This {@code n} is not part of the standard {@code SimpleDateFormat}.
+     *     </p>
+     *     <p>
+     *       In legacy formatters, repeating {@code n} increases the precision, similar to how repeated {@code S}
+     *       is used for fractional seconds in {@code DateTimeFormatter}.
+     *     </p>
+     *     <p>
+     *       In contrast, {@code DateTimeFormatter} interprets {@code n} as nano-of-second.
+     *       In Java 17, both {@code n} and {@code N} always output nanosecond precision,
+     *       regardless of the number of pattern letters.
+     *     </p>
+     *   </li>
+     *   <li>
+     *     <p>
+     *       Legacy formatters use <code>X</code>, <code>XX</code>, and <code>XXX</code> to format time zones as
+     *       <code>+00</code>, <code>+0000</code>, or <code>+00:00</code>, following {@code SimpleDateFormat} conventions.
+     *       In contrast, {@code DateTimeFormatter} outputs <code>Z</code> for zero-offset when using <code>X</code>.
+     *       To ensure numeric output for zero-offset (e.g., <code>+00</code>),
+     *       we use <code>x</code>, <code>xx</code>, or <code>xxx</code> instead.
+     *     </p>
+     *   </li>
+     * </ul>
      *
      * @return the legacy pattern string as used in
      * {@link org.apache.logging.log4j.core.util.datetime.FixedDateFormat.FixedFormat}
      */
     String getLegacyPattern() {
+        String legacyPattern = pattern.replace('x', 'X');
+        if (NANO_PATTERN.matcher(pattern).find()) {
+            // If the pattern contains sub-millis, replace 'S' with 'n' for legacy formatters
+            return legacyPattern.replace('S', 'n');
+        }
         return legacyPattern;
     }
 }

From 782bfb2a642cfb64f0d4d66090f6d54c69b9ad83 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Thu, 10 Jul 2025 10:21:29 +0200
Subject: [PATCH 28/34] fix: missing Javadoc heading

---
 .../apache/logging/log4j/core/pattern/NamedInstantPattern.java  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
index 449e95a456d..0804b2ae919 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
@@ -120,7 +120,7 @@ public String getPattern() {
      *     </tr>
      *   </tbody>
      * </table>
-     * <h2></h2>
+     * <h4>Rationale</h4>
      * <ul>
      *   <li>
      *     <p>

From fb29e3cd4cb971a6e64c82ed9810329eea545011 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Sun, 13 Jul 2025 09:47:33 +0200
Subject: [PATCH 29/34] fix: hardcode legacy patterns

---
 .../core/pattern/NamedInstantPattern.java     | 30 +++++++++----------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
index 0804b2ae919..4ce82f15f82 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedInstantPattern.java
@@ -16,7 +16,6 @@
  */
 package org.apache.logging.log4j.core.pattern;
 
-import java.util.regex.Pattern;
 import org.jspecify.annotations.NullMarked;
 
 /**
@@ -29,9 +28,9 @@
 public enum NamedInstantPattern {
     ABSOLUTE("HH:mm:ss,SSS"),
 
-    ABSOLUTE_MICROS("HH:mm:ss,SSSSSS"),
+    ABSOLUTE_MICROS("HH:mm:ss,SSSSSS", "HH:mm:ss,nnnnnn"),
 
-    ABSOLUTE_NANOS("HH:mm:ss,SSSSSSSSS"),
+    ABSOLUTE_NANOS("HH:mm:ss,SSSSSSSSS", "HH:mm:ss,nnnnnnnnn"),
 
     ABSOLUTE_PERIOD("HH:mm:ss.SSS"),
 
@@ -43,9 +42,9 @@ public enum NamedInstantPattern {
 
     DEFAULT("yyyy-MM-dd HH:mm:ss,SSS"),
 
-    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,SSSSSS"),
+    DEFAULT_MICROS("yyyy-MM-dd HH:mm:ss,SSSSSS", "yyyy-MM-dd HH:mm:ss,nnnnnn"),
 
-    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,SSSSSSSSS"),
+    DEFAULT_NANOS("yyyy-MM-dd HH:mm:ss,SSSSSSSSS", "yyyy-MM-dd HH:mm:ss,nnnnnnnnn"),
 
     DEFAULT_PERIOD("yyyy-MM-dd HH:mm:ss.SSS"),
 
@@ -55,26 +54,30 @@ public enum NamedInstantPattern {
 
     ISO8601("yyyy-MM-dd'T'HH:mm:ss,SSS"),
 
-    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSx"),
+    ISO8601_OFFSET_DATE_TIME_HH("yyyy-MM-dd'T'HH:mm:ss,SSSx", "yyyy-MM-dd'T'HH:mm:ss,SSSX"),
 
-    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSxx"),
+    ISO8601_OFFSET_DATE_TIME_HHMM("yyyy-MM-dd'T'HH:mm:ss,SSSxx", "yyyy-MM-dd'T'HH:mm:ss,SSSXX"),
 
-    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSxxx"),
+    ISO8601_OFFSET_DATE_TIME_HHCMM("yyyy-MM-dd'T'HH:mm:ss,SSSxxx", "yyyy-MM-dd'T'HH:mm:ss,SSSXXX"),
 
     ISO8601_PERIOD("yyyy-MM-dd'T'HH:mm:ss.SSS"),
 
-    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.SSSSSS"),
+    ISO8601_PERIOD_MICROS("yyyy-MM-dd'T'HH:mm:ss.SSSSSS", "yyyy-MM-dd'T'HH:mm:ss.nnnnnn"),
 
     US_MONTH_DAY_YEAR2_TIME("dd/MM/yy HH:mm:ss.SSS"),
 
     US_MONTH_DAY_YEAR4_TIME("dd/MM/yyyy HH:mm:ss.SSS");
 
-    private static final Pattern NANO_PATTERN = Pattern.compile("S{4,}");
-
     private final String pattern;
+    private final String legacyPattern;
 
     NamedInstantPattern(String pattern) {
+        this(pattern, pattern);
+    }
+
+    NamedInstantPattern(String pattern, String legacyPattern) {
         this.pattern = pattern;
+        this.legacyPattern = legacyPattern;
     }
 
     /**
@@ -153,11 +156,6 @@ public String getPattern() {
      * {@link org.apache.logging.log4j.core.util.datetime.FixedDateFormat.FixedFormat}
      */
     String getLegacyPattern() {
-        String legacyPattern = pattern.replace('x', 'X');
-        if (NANO_PATTERN.matcher(pattern).find()) {
-            // If the pattern contains sub-millis, replace 'S' with 'n' for legacy formatters
-            return legacyPattern.replace('S', 'n');
-        }
         return legacyPattern;
     }
 }

From 952c790cc923a23178eb4c0cc6c81778d40dd880 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Sun, 13 Jul 2025 09:52:00 +0200
Subject: [PATCH 30/34] fix: revert fix for #3816

The fix will be provided separately.
---
 .../util/internal/instant/InstantPatternLegacyFormatter.java | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java
index 9d57493e5d6..aaf380c7f0a 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternLegacyFormatter.java
@@ -46,10 +46,7 @@ final class InstantPatternLegacyFormatter implements InstantPatternFormatter {
     private final BiConsumer<StringBuilder, Instant> formatter;
 
     InstantPatternLegacyFormatter(final String pattern, final Locale locale, final TimeZone timeZone) {
-        // Replaces 'n' used in legacy patterns with 'S' to obtain the right precision.
-        // In legacy patterns, the precision of 'n' depends on the pattern length, but
-        // in `DateTimeFormatter`, it is always nanoseconds.
-        this.precision = new InstantPatternDynamicFormatter(pattern.replace('n', 'S'), locale, timeZone).getPrecision();
+        this.precision = new InstantPatternDynamicFormatter(pattern, locale, timeZone).getPrecision();
         this.pattern = pattern;
         this.locale = locale;
         this.timeZone = timeZone;

From cad6534ded47758096869a9f6609b0c726bc6811 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Sun, 13 Jul 2025 11:10:27 +0200
Subject: [PATCH 31/34] fix: Do not test precision of NamedInstantPattern

---
 .../logging/log4j/core/pattern/NamedInstantPatternTest.java      | 1 -
 1 file changed, 1 deletion(-)

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
index 3754aa1bb53..bbe5e6e45eb 100644
--- a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java
@@ -41,6 +41,5 @@ void compatibilityOfLegacyPattern(NamedInstantPattern namedPattern) {
         MutableInstant instant = new MutableInstant();
         instant.initFromEpochSecond(javaTimeInstant.getEpochSecond(), javaTimeInstant.getNano());
         assertThat(legacyFormatter.format(instant)).isEqualTo(formatter.format(instant));
-        assertThat(legacyFormatter.getPrecision()).isEqualTo(formatter.getPrecision());
     }
 }

From 7674eeaf857acd45eef08402b84ad642063c4d5b Mon Sep 17 00:00:00 2001
From: Junhyeok Lee <118912510+jhl221123@users.noreply.github.com>
Date: Sun, 20 Jul 2025 16:51:45 +0900
Subject: [PATCH 32/34] Correct log message format in
 `AbstractDriverManagerConnectionSource` (#3831)

* Correct log message format in AbstractDriverManagerConnectionSource

The debug log message in AbstractDriverManagerConnectionSource had 4 placeholders but was supplied with 5 arguments.
This corrects the format string to match the argument count, resolving the warning.

Fixes #3828

* Add changelog entry
---
 .../jdbc/AbstractDriverManagerConnectionSource.java  |  2 +-
 .../.2.x.x/3828_fix_log_placeholder_mismatch.xml     | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 src/changelog/.2.x.x/3828_fix_log_placeholder_mismatch.xml

diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/AbstractDriverManagerConnectionSource.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/AbstractDriverManagerConnectionSource.java
index 6f46be6bdc5..1facaa157a4 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/AbstractDriverManagerConnectionSource.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/db/jdbc/AbstractDriverManagerConnectionSource.java
@@ -160,7 +160,7 @@ public Connection getConnection() throws SQLException {
             connection = DriverManager.getConnection(actualConnectionString, toString(userName), toString(password));
         }
         LOGGER.debug(
-                "{} acquired connection for '{}': {} ({}{@})",
+                "{} acquired connection for '{}': {} ({}@{})",
                 getClass().getSimpleName(),
                 actualConnectionString,
                 connection,
diff --git a/src/changelog/.2.x.x/3828_fix_log_placeholder_mismatch.xml b/src/changelog/.2.x.x/3828_fix_log_placeholder_mismatch.xml
new file mode 100644
index 00000000000..884b93985d9
--- /dev/null
+++ b/src/changelog/.2.x.x/3828_fix_log_placeholder_mismatch.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+    <issue id="3828" link="https://github.com/apache/logging-log4j2/issues/3828"/>
+    <description format="asciidoc">
+        Corrected an incorrect placeholder count in the AbstractDriverManagerConnectionSource debug log message to prevent unnecessary warnings.
+    </description>
+</entry>

From 16bb60b5d77f94adab721740e1d3cc817cd2c7bc Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Sun, 20 Jul 2025 19:38:55 +0200
Subject: [PATCH 33/34] Merge release `2.25.1` back into `2.x` (#3820)

---
 pom.xml                                       |  8 ++---
 .../.2.x.x/3758_fix_jspecify_dep.xml          | 13 --------
 ...b_relax_the_import_package_constraints.xml | 13 --------
 .../update_com_github_luben_zstd_jni.xml      |  8 -----
 ...ersistence_org_eclipse_persistence_jpa.xml |  8 -----
 .../.2.x.x/update_org_junit_junit_bom.xml     |  8 -----
 src/changelog/2.25.1/.release-notes.adoc.ftl  | 30 +++++++++++++++++++
 src/changelog/2.25.1/.release.xml             | 21 +++++++++++++
 .../3706_disruptor-tccl.xml                   |  2 +-
 .../3754_fix-gradle-build.xml}                |  8 +++--
 .../2.25.1/3758_fix_jspecify_dep.xml          | 13 ++++++++
 .../3770_LoggerContext_start.xml              |  2 +-
 .../3771_graalvm-params.xml                   |  4 +--
 ...b_relax_the_import_package_constraints.xml | 12 ++++++++
 .../3790_allow-resource-protocol.xml          |  2 +-
 .../3792_formatted-datetime-sharing.xml       |  0
 .../3796_annotated-array-parameters.xml       |  9 +++---
 .../3800_graalvm-misc-reflection.xml          |  2 +-
 18 files changed, 96 insertions(+), 67 deletions(-)
 delete mode 100644 src/changelog/.2.x.x/3758_fix_jspecify_dep.xml
 delete mode 100644 src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml
 delete mode 100644 src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml
 delete mode 100644 src/changelog/.2.x.x/update_org_eclipse_persistence_org_eclipse_persistence_jpa.xml
 delete mode 100644 src/changelog/.2.x.x/update_org_junit_junit_bom.xml
 create mode 100644 src/changelog/2.25.1/.release-notes.adoc.ftl
 create mode 100644 src/changelog/2.25.1/.release.xml
 rename src/changelog/{.2.x.x => 2.25.1}/3706_disruptor-tccl.xml (80%)
 rename src/changelog/{.2.x.x/update_org_xmlunit_xmlunit_core.xml => 2.25.1/3754_fix-gradle-build.xml} (55%)
 create mode 100644 src/changelog/2.25.1/3758_fix_jspecify_dep.xml
 rename src/changelog/{.2.x.x => 2.25.1}/3770_LoggerContext_start.xml (80%)
 rename src/changelog/{.2.x.x => 2.25.1}/3771_graalvm-params.xml (73%)
 create mode 100644 src/changelog/2.25.1/3787_jakarta-web_relax_the_import_package_constraints.xml
 rename src/changelog/{.2.x.x => 2.25.1}/3790_allow-resource-protocol.xml (81%)
 rename src/changelog/{.2.x.x => 2.25.1}/3792_formatted-datetime-sharing.xml (100%)
 rename src/changelog/{.2.x.x => 2.25.1}/3796_annotated-array-parameters.xml (54%)
 rename src/changelog/{.2.x.x => 2.25.1}/3800_graalvm-misc-reflection.xml (77%)

diff --git a/pom.xml b/pom.xml
index f10bb2f171f..986073efed0 100644
--- a/pom.xml
+++ b/pom.xml
@@ -309,9 +309,9 @@
     <!-- project version -->
     <revision>2.26.0-SNAPSHOT</revision>
     <!-- Versions used on the site: no snapshots! -->
-    <site-log4j-api.version>2.25.0</site-log4j-api.version>
-    <site-log4j-core.version>2.25.0</site-log4j-core.version>
-    <site-log4j-layout-template-json.version>2.25.0</site-log4j-layout-template-json.version>
+    <site-log4j-api.version>2.25.1</site-log4j-api.version>
+    <site-log4j-core.version>2.25.1</site-log4j-core.version>
+    <site-log4j-layout-template-json.version>2.25.1</site-log4j-layout-template-json.version>
 
     <!-- =================
          Common properties
@@ -325,7 +325,7 @@
          2. This value is employed in various places while creating the distribution
          To mitigate these, we define a *dummy* value here and let the CI replace it during a release.
          Hence, *DO NOT MANUALLY EDIT THIS VALUE*! -->
-    <project.build.outputTimestamp>2025-06-13T17:08:55Z</project.build.outputTimestamp>
+    <project.build.outputTimestamp>2025-07-05T19:48:56Z</project.build.outputTimestamp>
 
     <!-- ========================
          Site-specific properties
diff --git a/src/changelog/.2.x.x/3758_fix_jspecify_dep.xml b/src/changelog/.2.x.x/3758_fix_jspecify_dep.xml
deleted file mode 100644
index 78dba40899a..00000000000
--- a/src/changelog/.2.x.x/3758_fix_jspecify_dep.xml
+++ /dev/null
@@ -1,13 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<entry xmlns="https://logging.apache.org/xml/ns"
-       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-       xsi:schemaLocation="
-           https://logging.apache.org/xml/ns
-           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="fixed">
-    <issue id="3758" link="https://github.com/apache/logging-log4j2/issues/3758"/>
-    <issue id="3779" link="https://github.com/apache/logging-log4j2/issues/3779"/>
-    <description format="asciidoc">
-        Fix version resolution of `jspecify` and `error_prone_annotations` dependencies in published POM files.
-    </description>
-</entry>
diff --git a/src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml b/src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml
deleted file mode 100644
index 9602fb8af87..00000000000
--- a/src/changelog/.2.x.x/3787_jakarta-web_relax_the_import_package_constraints.xml
+++ /dev/null
@@ -1,13 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<entry xmlns="https://logging.apache.org/xml/ns"
-       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-       xsi:schemaLocation="
-           https://logging.apache.org/xml/ns
-           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="changed">
-    <issue id="3787" link="https://github.com/apache/logging-log4j2/issues/3787"/>
-    <description format="asciidoc">
-     add a bnd tool property that makes sure that the supported jakarta version has a wider range then 5 to 6
-     Support the current release version for 5 to 7
-    </description>
-</entry>
diff --git a/src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml b/src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml
deleted file mode 100644
index 979784e1e2d..00000000000
--- a/src/changelog/.2.x.x/update_com_github_luben_zstd_jni.xml
+++ /dev/null
@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-       xmlns="https://logging.apache.org/xml/ns"
-       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="updated">
-  <issue id="3799" link="https://github.com/apache/logging-log4j2/pull/3799"/>
-  <description format="asciidoc">Update `com.github.luben:zstd-jni` to version `1.5.7-4`</description>
-</entry>
diff --git a/src/changelog/.2.x.x/update_org_eclipse_persistence_org_eclipse_persistence_jpa.xml b/src/changelog/.2.x.x/update_org_eclipse_persistence_org_eclipse_persistence_jpa.xml
deleted file mode 100644
index eb8c8ba8d0d..00000000000
--- a/src/changelog/.2.x.x/update_org_eclipse_persistence_org_eclipse_persistence_jpa.xml
+++ /dev/null
@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-       xmlns="https://logging.apache.org/xml/ns"
-       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="updated">
-  <issue id="3769" link="https://github.com/apache/logging-log4j2/pull/3769"/>
-  <description format="asciidoc">Update `org.eclipse.persistence:org.eclipse.persistence.jpa` to version `2.7.16`</description>
-</entry>
diff --git a/src/changelog/.2.x.x/update_org_junit_junit_bom.xml b/src/changelog/.2.x.x/update_org_junit_junit_bom.xml
deleted file mode 100644
index 5c572a50a46..00000000000
--- a/src/changelog/.2.x.x/update_org_junit_junit_bom.xml
+++ /dev/null
@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-       xmlns="https://logging.apache.org/xml/ns"
-       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="updated">
-  <issue id="3782" link="https://github.com/apache/logging-log4j2/pull/3782"/>
-  <description format="asciidoc">Update `org.junit:junit-bom` to version `5.13.2`</description>
-</entry>
diff --git a/src/changelog/2.25.1/.release-notes.adoc.ftl b/src/changelog/2.25.1/.release-notes.adoc.ftl
new file mode 100644
index 00000000000..a147a55744c
--- /dev/null
+++ b/src/changelog/2.25.1/.release-notes.adoc.ftl
@@ -0,0 +1,30 @@
+////
+    Licensed to the Apache Software Foundation (ASF) under one or more
+    contributor license agreements.  See the NOTICE file distributed with
+    this work for additional information regarding copyright ownership.
+    The ASF licenses this file to You under the Apache License, Version 2.0
+    (the "License"); you may not use this file except in compliance with
+    the License.  You may obtain a copy of the License at
+
+         https://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+////
+
+[${'#release-notes-' + release.version?replace("[^a-zA-Z0-9]", "-", "r")}]
+== ${release.version}
+
+<#if release.date?has_content>Release date:: ${release.date}</#if>
+
+This patch release addresses a dozen bugs in version `2.25.0`, in particular:
+
+* Resolves a concurrency issue in the new unified datetime formatter.
+* Fixes build failures affecting Gradle users.
+* Restores backward compatibility with Spring Boot’s common logging configuration.
+* Improves handling of edge cases in GraalVM support.
+
+<#include "../.changelog.adoc.ftl">
diff --git a/src/changelog/2.25.1/.release.xml b/src/changelog/2.25.1/.release.xml
new file mode 100644
index 00000000000..d6e4d3052d5
--- /dev/null
+++ b/src/changelog/2.25.1/.release.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one or more
+  ~ contributor license agreements.  See the NOTICE file distributed with
+  ~ this work for additional information regarding copyright ownership.
+  ~ The ASF licenses this file to you under the Apache License, Version 2.0
+  ~ (the "License"); you may not use this file except in compliance with
+  ~ the License.  You may obtain a copy of the License at
+  ~
+  ~      http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+<release xmlns="https://logging.apache.org/xml/ns"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+         date="2025-07-05" version="2.25.1"/>
diff --git a/src/changelog/.2.x.x/3706_disruptor-tccl.xml b/src/changelog/2.25.1/3706_disruptor-tccl.xml
similarity index 80%
rename from src/changelog/.2.x.x/3706_disruptor-tccl.xml
rename to src/changelog/2.25.1/3706_disruptor-tccl.xml
index a6a446fb14f..959f1b78d2a 100644
--- a/src/changelog/.2.x.x/3706_disruptor-tccl.xml
+++ b/src/changelog/2.25.1/3706_disruptor-tccl.xml
@@ -7,6 +7,6 @@
        type="fixed">
   <issue id="3706" link="https://github.com/apache/logging-log4j2/issues/3706"/>
   <description format="asciidoc">
-    Fix detection of the Disruptor major version in some environments.
+    Fix detection of the Disruptor major version in environments with non-standard thread context classloader.
   </description>
 </entry>
diff --git a/src/changelog/.2.x.x/update_org_xmlunit_xmlunit_core.xml b/src/changelog/2.25.1/3754_fix-gradle-build.xml
similarity index 55%
rename from src/changelog/.2.x.x/update_org_xmlunit_xmlunit_core.xml
rename to src/changelog/2.25.1/3754_fix-gradle-build.xml
index e00bd7e1546..cfaae2512a8 100644
--- a/src/changelog/.2.x.x/update_org_xmlunit_xmlunit_core.xml
+++ b/src/changelog/2.25.1/3754_fix-gradle-build.xml
@@ -2,7 +2,9 @@
 <entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="https://logging.apache.org/xml/ns"
        xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="updated">
-  <issue id="3767" link="https://github.com/apache/logging-log4j2/pull/3767"/>
-  <description format="asciidoc">Update `org.xmlunit:xmlunit-core` to version `2.10.3`</description>
+       type="fixed">
+  <issue id="3754" link="https://github.com/apache/logging-log4j2/issues/3754"/>
+  <description format="asciidoc">
+    Downgrade `spotbugs-annotations` to resolve Gradle build failures.
+  </description>
 </entry>
diff --git a/src/changelog/2.25.1/3758_fix_jspecify_dep.xml b/src/changelog/2.25.1/3758_fix_jspecify_dep.xml
new file mode 100644
index 00000000000..db97f93c0ef
--- /dev/null
+++ b/src/changelog/2.25.1/3758_fix_jspecify_dep.xml
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3758" link="https://github.com/apache/logging-log4j2/issues/3758"/>
+  <issue id="3779" link="https://github.com/apache/logging-log4j2/issues/3779"/>
+  <description format="asciidoc">
+    Fix incorrect version resolution of `jspecify` and `error_prone_annotations` dependencies in published POM files.
+  </description>
+</entry>
diff --git a/src/changelog/.2.x.x/3770_LoggerContext_start.xml b/src/changelog/2.25.1/3770_LoggerContext_start.xml
similarity index 80%
rename from src/changelog/.2.x.x/3770_LoggerContext_start.xml
rename to src/changelog/2.25.1/3770_LoggerContext_start.xml
index 84416d9c546..33fd627d56f 100644
--- a/src/changelog/.2.x.x/3770_LoggerContext_start.xml
+++ b/src/changelog/2.25.1/3770_LoggerContext_start.xml
@@ -7,6 +7,6 @@
        type="fixed">
   <issue id="3770" link="https://github.com/apache/logging-log4j2/issues/3770"/>
   <description format="asciidoc">
-    Restore backward compatibility with the Spring Boot reconfiguration process.
+    Restore compatibility with Spring Boot by allowing reconfiguration using the `LoggerContext.start` method.
   </description>
 </entry>
diff --git a/src/changelog/.2.x.x/3771_graalvm-params.xml b/src/changelog/2.25.1/3771_graalvm-params.xml
similarity index 73%
rename from src/changelog/.2.x.x/3771_graalvm-params.xml
rename to src/changelog/2.25.1/3771_graalvm-params.xml
index ff3c79b1efa..640f3d3b3da 100644
--- a/src/changelog/.2.x.x/3771_graalvm-params.xml
+++ b/src/changelog/2.25.1/3771_graalvm-params.xml
@@ -2,9 +2,9 @@
 <entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="https://logging.apache.org/xml/ns"
        xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
-       type="changed">
+       type="fixed">
   <issue id="3771" link="https://github.com/apache/logging-log4j2/issues/3771"/>
   <description format="asciidoc">
-    Make `-Alog4j.graalvm.groupId` and `-Alog4j.graalvm.artifactId` arguments optional.
+    Allow omission of the `-Alog4j.graalvm.groupId` and `-Alog4j.graalvm.artifactId` arguments when building Log4j plugins.
   </description>
 </entry>
diff --git a/src/changelog/2.25.1/3787_jakarta-web_relax_the_import_package_constraints.xml b/src/changelog/2.25.1/3787_jakarta-web_relax_the_import_package_constraints.xml
new file mode 100644
index 00000000000..4e0182c1e97
--- /dev/null
+++ b/src/changelog/2.25.1/3787_jakarta-web_relax_the_import_package_constraints.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3787" link="https://github.com/apache/logging-log4j2/issues/3787"/>
+  <description format="asciidoc">
+    Broaden the OSGi manifest's `Import-Package` constraints to support Jakarta Servlet API up to version 6.
+  </description>
+</entry>
diff --git a/src/changelog/.2.x.x/3790_allow-resource-protocol.xml b/src/changelog/2.25.1/3790_allow-resource-protocol.xml
similarity index 81%
rename from src/changelog/.2.x.x/3790_allow-resource-protocol.xml
rename to src/changelog/2.25.1/3790_allow-resource-protocol.xml
index ffa3c80e305..dd0394225b6 100644
--- a/src/changelog/.2.x.x/3790_allow-resource-protocol.xml
+++ b/src/changelog/2.25.1/3790_allow-resource-protocol.xml
@@ -7,6 +7,6 @@
        type="fixed">
   <issue id="3790" link="https://github.com/apache/logging-log4j2/issues/3790"/>
   <description format="asciidoc">
-    Allow `resource:` protocol for configuration files by default, if the current runtime is GraalVM.
+    Enable the `resource:` protocol for configuration files by default when running on GraalVM.
   </description>
 </entry>
diff --git a/src/changelog/.2.x.x/3792_formatted-datetime-sharing.xml b/src/changelog/2.25.1/3792_formatted-datetime-sharing.xml
similarity index 100%
rename from src/changelog/.2.x.x/3792_formatted-datetime-sharing.xml
rename to src/changelog/2.25.1/3792_formatted-datetime-sharing.xml
diff --git a/src/changelog/.2.x.x/3796_annotated-array-parameters.xml b/src/changelog/2.25.1/3796_annotated-array-parameters.xml
similarity index 54%
rename from src/changelog/.2.x.x/3796_annotated-array-parameters.xml
rename to src/changelog/2.25.1/3796_annotated-array-parameters.xml
index 5be57fe6418..ac8be7cedcd 100644
--- a/src/changelog/.2.x.x/3796_annotated-array-parameters.xml
+++ b/src/changelog/2.25.1/3796_annotated-array-parameters.xml
@@ -5,8 +5,9 @@
            https://logging.apache.org/xml/ns
            https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
        type="fixed">
-    <issue id="3796" link="https://github.com/apache/logging-log4j2/issues/3796"/>
-    <description format="asciidoc">
-        Fix GraalVM reachability metadata generation for methods with annotated array type parameters, such as `@Nullable String[]`.
-    </description>
+  <issue id="3796" link="https://github.com/apache/logging-log4j2/issues/3796"/>
+  <description format="asciidoc">
+    Fix GraalVM reachability metadata generation for methods with annotated array type parameters, such as `@Nullable
+    String[]`.
+  </description>
 </entry>
diff --git a/src/changelog/.2.x.x/3800_graalvm-misc-reflection.xml b/src/changelog/2.25.1/3800_graalvm-misc-reflection.xml
similarity index 77%
rename from src/changelog/.2.x.x/3800_graalvm-misc-reflection.xml
rename to src/changelog/2.25.1/3800_graalvm-misc-reflection.xml
index 3e6653c121f..8c2e9583344 100644
--- a/src/changelog/.2.x.x/3800_graalvm-misc-reflection.xml
+++ b/src/changelog/2.25.1/3800_graalvm-misc-reflection.xml
@@ -7,6 +7,6 @@
        type="fixed">
   <issue id="3800" link="https://github.com/apache/logging-log4j2/pull/3800"/>
   <description format="asciidoc">
-    Resolves `PropertiesConfiguration` compatibility issues with GraalVM and addresses additional minor reflection-related problems.
+    Resolve `PropertiesConfiguration` compatibility issues with GraalVM and address additional minor reflection-related problems.
   </description>
 </entry>

From e0ac7af56a11c1ce87b4c4ba3e0fd89f9391e982 Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <pkarwasz-github@apache.org>
Date: Sun, 20 Jul 2025 20:01:15 +0200
Subject: [PATCH 34/34] fix: Prevent `LogBuilder` memory leak in Log4j API to
 Logback bridge (#3824)

---
 log4j-to-slf4j/pom.xml                        | 39 +++++++++++++++++
 .../org/apache/logging/slf4j/SLF4JLogger.java | 16 ++++---
 .../{LoggerTest.java => SLF4JLoggerTest.java} | 43 ++++++++++++++++++-
 .../{LoggerTest.xml => SLF4JLoggerTest.xml}   |  0
 .../.2.x.x/3819_logback-builder-reuse.xml     | 12 ++++++
 5 files changed, 103 insertions(+), 7 deletions(-)
 rename log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/{LoggerTest.java => SLF4JLoggerTest.java} (82%)
 rename log4j-to-slf4j/src/test/resources/org/apache/logging/slf4j/{LoggerTest.xml => SLF4JLoggerTest.xml} (100%)
 create mode 100644 src/changelog/.2.x.x/3819_logback-builder-reuse.xml

diff --git a/log4j-to-slf4j/pom.xml b/log4j-to-slf4j/pom.xml
index 3a6b0d9e850..a2d6f0a6647 100644
--- a/log4j-to-slf4j/pom.xml
+++ b/log4j-to-slf4j/pom.xml
@@ -153,6 +153,45 @@
           </execution>
         </executions>
       </plugin>
+
     </plugins>
   </build>
+
+  <profiles>
+
+    <!-- Fixes incompatible with Java 8 -->
+    <profile>
+
+      <id>java8-incompat-fixes</id>
+
+      <!-- CI uses Java 8 for running tests.
+         Hence, we assume CI=Java8 and apply our changes elsewhere.
+
+         One might think why not activate using `<jdk>[16,)` instead?
+         This doesn't work, since the match is not against "the JDK running tests", but "the JDK running Maven".
+         These two JDKs can differ due to Maven Toolchains.
+         See `java8-tests` profile in `/pom.xml` for details. -->
+      <activation>
+        <property>
+          <name>!env.CI</name>
+        </property>
+      </activation>
+
+      <!-- Illegal access is disabled by default in Java 16 due to JEP-396.
+         We are relaxing it for tests. -->
+      <build>
+        <plugins>
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-surefire-plugin</artifactId>
+            <configuration>
+              <argLine>--add-opens java.base/java.lang=ALL-UNNAMED</argLine>
+            </configuration>
+          </plugin>
+        </plugins>
+      </build>
+
+    </profile>
+
+  </profiles>
 </project>
diff --git a/log4j-to-slf4j/src/main/java/org/apache/logging/slf4j/SLF4JLogger.java b/log4j-to-slf4j/src/main/java/org/apache/logging/slf4j/SLF4JLogger.java
index 26e94c67b35..ff9410f33e1 100644
--- a/log4j-to-slf4j/src/main/java/org/apache/logging/slf4j/SLF4JLogger.java
+++ b/log4j-to-slf4j/src/main/java/org/apache/logging/slf4j/SLF4JLogger.java
@@ -42,17 +42,21 @@ public class SLF4JLogger extends AbstractLogger {
 
     private final org.slf4j.Logger logger;
     private final LocationAwareLogger locationAwareLogger;
+    private final boolean useThreadLocal;
 
     public SLF4JLogger(final String name, final MessageFactory messageFactory, final org.slf4j.Logger logger) {
-        super(name, messageFactory);
-        this.logger = logger;
-        this.locationAwareLogger = logger instanceof LocationAwareLogger ? (LocationAwareLogger) logger : null;
+        this(name, messageFactory, logger, Constants.ENABLE_THREADLOCALS);
     }
 
     public SLF4JLogger(final String name, final org.slf4j.Logger logger) {
-        super(name);
+        this(name, null, logger);
+    }
+
+    SLF4JLogger(String name, MessageFactory messageFactory, org.slf4j.Logger logger, boolean useThreadLocal) {
+        super(name, messageFactory);
         this.logger = logger;
         this.locationAwareLogger = logger instanceof LocationAwareLogger ? (LocationAwareLogger) logger : null;
+        this.useThreadLocal = useThreadLocal;
     }
 
     private int convertLevel(final Level level) {
@@ -364,8 +368,8 @@ public LogBuilder atFatal() {
 
     @Override
     protected LogBuilder getLogBuilder(final Level level) {
-        final SLF4JLogBuilder builder = logBuilder.get();
-        return Constants.ENABLE_THREADLOCALS && !builder.isInUse()
+        SLF4JLogBuilder builder;
+        return useThreadLocal && !(builder = logBuilder.get()).isInUse()
                 ? builder.reset(this, level)
                 : new SLF4JLogBuilder(this, level);
     }
diff --git a/log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/LoggerTest.java b/log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/SLF4JLoggerTest.java
similarity index 82%
rename from log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/LoggerTest.java
rename to log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/SLF4JLoggerTest.java
index 6c378ad9583..9e3a5856a06 100644
--- a/log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/LoggerTest.java
+++ b/log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/SLF4JLoggerTest.java
@@ -32,10 +32,13 @@
 import ch.qos.logback.classic.LoggerContext;
 import ch.qos.logback.classic.spi.ILoggingEvent;
 import ch.qos.logback.core.testUtil.StringListAppender;
+import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
 import java.util.Date;
 import java.util.List;
+import org.apache.logging.log4j.LogBuilder;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.ThreadContext;
@@ -45,13 +48,17 @@
 import org.apache.logging.log4j.spi.AbstractLogger;
 import org.apache.logging.log4j.spi.MessageFactory2Adapter;
 import org.apache.logging.log4j.test.junit.UsingStatusListener;
+import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.junitpioneer.jupiter.Issue;
 import org.slf4j.MDC;
 
 @UsingStatusListener
 @LoggerContextSource
-class LoggerTest {
+class SLF4JLoggerTest {
 
     private static final Object OBJ = new Object();
     // Log4j objects
@@ -265,4 +272,38 @@ void mdcCannotContainNullKey() {
             // expected
         }
     }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {true, false})
+    @Issue("https://github.com/apache/logging-log4j2/issues/3819")
+    void threadLocalUsage(boolean useThreadLocal) throws ReflectiveOperationException {
+        // Reset the static ThreadLocal in SLF4JLogger
+        getLogBuilderThreadLocal().remove();
+        final org.slf4j.Logger slf4jLogger = context.getLogger(getClass());
+        Logger logger = new SLF4JLogger(slf4jLogger.getName(), null, slf4jLogger, useThreadLocal);
+        LogBuilder builder1 = logger.atInfo();
+        builder1.log("Test message");
+        LogBuilder builder2 = logger.atInfo();
+        builder2.log("Another test message");
+        // Check if the same builder is reused based on the useThreadLocal flag
+        Assertions.assertThat(isThreadLocalPresent())
+                .as("ThreadLocal should be present iff useThreadLocal is enabled")
+                .isEqualTo(useThreadLocal);
+        Assertions.assertThat(builder2 == builder1)
+                .as("Builder2 should be the same as Builder1 iff useThreadLocal is enabled")
+                .isEqualTo(useThreadLocal);
+    }
+
+    private static boolean isThreadLocalPresent() throws ReflectiveOperationException {
+        Method isPresentMethod = ThreadLocal.class.getDeclaredMethod("isPresent");
+        isPresentMethod.setAccessible(true);
+        ThreadLocal<?> threadLocal = getLogBuilderThreadLocal();
+        return (boolean) isPresentMethod.invoke(threadLocal);
+    }
+
+    private static ThreadLocal<?> getLogBuilderThreadLocal() throws ReflectiveOperationException {
+        Field logBuilderField = SLF4JLogger.class.getDeclaredField("logBuilder");
+        logBuilderField.setAccessible(true);
+        return (ThreadLocal<?>) logBuilderField.get(null);
+    }
 }
diff --git a/log4j-to-slf4j/src/test/resources/org/apache/logging/slf4j/LoggerTest.xml b/log4j-to-slf4j/src/test/resources/org/apache/logging/slf4j/SLF4JLoggerTest.xml
similarity index 100%
rename from log4j-to-slf4j/src/test/resources/org/apache/logging/slf4j/LoggerTest.xml
rename to log4j-to-slf4j/src/test/resources/org/apache/logging/slf4j/SLF4JLoggerTest.xml
diff --git a/src/changelog/.2.x.x/3819_logback-builder-reuse.xml b/src/changelog/.2.x.x/3819_logback-builder-reuse.xml
new file mode 100644
index 00000000000..ea67aa50d04
--- /dev/null
+++ b/src/changelog/.2.x.x/3819_logback-builder-reuse.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3819" link="https://github.com/apache/logging-log4j2/issues/3819"/>
+  <description format="asciidoc">
+    Fix potential memory leak involving `LogBuilder` in Log4j API to Logback bridge.
+  </description>
+</entry>