Create NamedInstantPattern to make date & time patterns supported by Pattern Layout programmatically accessible

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();
     }
 
     /**
@@ -140,53 +140,14 @@ 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) {

log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/NamedPattern.java

@@ -0,0 +1,56 @@
+/*
+ * 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")
+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;
+    }
+
+    public String getLegacyPattern() {
+        return legacyPattern;
+    }
+
+    public String getNonLegacyPattern() {
+        return nonLegacyPattern;
+    }
+}

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>