Add documentation for jvmrunargs lookup and verify functionality in 2.25.0

- Documented `jvmrunargs` lookup in `lookups.adoc` with usage examples.
- Verified that the lookup works correctly in Log4j 2.25.0 using sample app and JVM args.
- Included example configuration demonstrating retrieval of JVM runtime arguments.

Closes apache#2726

Author: ramanathan1504

log4j-core-test/src/test/java/org/apache/logging/log4j/core/lookup/JvmRunArgsIntegrationTest.java

@@ -18,12 +18,12 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 public class JvmRunArgsIntegrationTest {
     @Test
     public void testJvmRunArgsInConfig() {
         Logger logger = LogManager.getLogger(JvmRunArgsIntegrationTest.class);
         logger.info("Testing JVM Args lookup in config");
     }
-}
+}

log4j-core-test/src/test/java/org/apache/logging/log4j/core/lookup/JvmRunArgsLookupTest.java

@@ -16,19 +16,19 @@
  */
 package org.apache.logging.log4j.core.lookup;
 
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNull;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 import org.apache.logging.log4j.core.LogEvent;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 public class JvmRunArgsLookupTest {
 
     @Test
     public void testJvmRunArgsLookupIsRegistered() {
         Interpolator interpolator = new Interpolator();
         StrLookup lookup = interpolator.getStrLookupMap().get("jvmrunargs");
-        assertNotNull("jvmrunargs lookup should be registered", lookup);
+        assertNotNull(lookup, "jvmrunargs lookup should be registered");
     }
 
     @Test
@@ -41,4 +41,4 @@ public void testJvmRunArgsLookupReturnsArgs() {
         // Most likely null unless -Xmx is set
         assertNull(anyArg);
     }
-}
+}

log4j-core/src/main/java/org/apache/logging/log4j/core/lookup/Interpolator.java

@@ -93,14 +93,6 @@ public Interpolator(final StrLookup defaultLookup, final List<String> pluginPack
                 handleError(entry.getKey(), t);
             }
         }
-
-        if (!strLookupMap.containsKey(LOOKUP_KEY_JVMRUNARGS)) {
-            try {
-                strLookupMap.put(LOOKUP_KEY_JVMRUNARGS, new JmxRuntimeInputArgumentsLookup());
-            } catch (Throwable t) {
-                handleError(LOOKUP_KEY_JVMRUNARGS, t);
-            }
-        }
     }
 
     /**

src/site/antora/modules/ROOT/pages/manual/lookups.adoc

@@ -1052,3 +1052,41 @@ You can check out the following files for examples:
 
 * {project-github-url}/log4j-core/src/main/java/org/apache/logging/log4j/core/lookup/LowerLookup.java[`LowerLookup.java`] – <<LowerLookup>> lower-cases its input
 * {project-github-url}/log4j-core/src/main/java/org/apache/logging/log4j/core/lookup/EventLookup.java[`EventLookup.java`] – <<EventLookup>> extracts specified fields from the effective `LogEvent` in the context
+
+[[JVMRunArgsLookup]]
+== JVM Runtime Arguments Lookup
+
+The `jvmrunargs` lookup allows retrieval of the JVM runtime arguments
+passed to the Java process at startup.
+
+=== Usage
+
+Use the `${jvmrunargs:<index>}` syntax, where `<index>` is the zero-based
+position of the JVM argument to retrieve.
+
+For example:
+
+[source,xml]
+----
+<Appenders>
+    <Console name="Console" target="SYSTEM_OUT">
+        <PatternLayout pattern="JVM Arg[0]: ${jvmrunargs:0} %m%n" />
+    </Console>
+</Appenders>
+----
+
+If the specified index is out of range, the lookup returns `null`.
+
+=== Example Output
+
+Given the following JVM startup arguments:
+
+The lookup expressions would produce:
+
+- `${jvmrunargs:0}` → `-DexampleArg=value`
+- `${jvmrunargs:1}` → `-Xmx512m`
+
+=== Notes
+
+* This lookup was fixed in version 2.25.0.
+* If no JVM arguments are available, all lookups will return `null`.