Log4jLog re-resolves ExtendedLogger on deserialization

This is necessary for compatibility with Log4J 2.21, analogous to the existing re-resolution in Spring's SLF4J adapter.

Closes gh-31582

Author: jhoeller

Diff for: spring-jcl/src/main/java/org/apache/commons/logging/LogAdapter.java

@@ -145,9 +145,12 @@ private static class Log4jLog implements Log, Serializable {
 		private static final LoggerContext loggerContext =
 				LogManager.getContext(Log4jLog.class.getClassLoader(), false);
 
-		private final ExtendedLogger logger;
+		private final String name;
+
+		private final transient ExtendedLogger logger;
 
 		public Log4jLog(String name) {
+			this.name = name;
 			LoggerContext context = loggerContext;
 			if (context == null) {
 				// Circular call in early-init scenario -> static field not initialized yet
@@ -261,6 +264,10 @@ private void log(Level level, Object message, Throwable exception) {
 				this.logger.logIfEnabled(FQCN, level, null, message, exception);
 			}
 		}
+
+		protected Object readResolve() {
+			return new Log4jLog(this.name);
+		}
 	}