Register Log42J StatusListener

Update Log42JLoggingSystem to register Boot's StatusListener
instead of resetting the fallbackListener during initialization.

This fixes an issue when resetting the fallback listener leads to
closing standard streams.

See gh-43963

Signed-off-by: Dmytro Nosan <[email protected]>

Author: nosan

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java

@@ -47,6 +47,7 @@
 import org.apache.logging.log4j.core.util.AuthorizationProvider;
 import org.apache.logging.log4j.core.util.NameUtil;
 import org.apache.logging.log4j.jul.Log4jBridgeHandler;
+import org.apache.logging.log4j.status.StatusConsoleListener;
 import org.apache.logging.log4j.status.StatusLogger;
 import org.apache.logging.log4j.util.PropertiesUtil;
 
@@ -93,6 +94,9 @@ public class Log4J2LoggingSystem extends AbstractLoggingSystem {
 	static final String ENVIRONMENT_KEY = Conventions.getQualifiedAttributeName(Log4J2LoggingSystem.class,
 			"environment");
 
+	static final String STATUS_LISTENER_KEY = Conventions.getQualifiedAttributeName(Log4J2LoggingSystem.class,
+			"statusListener");
+
 	private static final LogLevels<Level> LEVELS = new LogLevels<>();
 
 	static {
@@ -214,7 +218,9 @@ public void initialize(LoggingInitializationContext initializationContext, Strin
 		if (isAlreadyInitialized(loggerContext)) {
 			return;
 		}
-		resetFallbackListenerStream(StatusLogger.getLogger());
+		StatusConsoleListener listener = new StatusConsoleListener(Level.WARN);
+		StatusLogger.getLogger().registerListener(listener);
+		getLoggerContext().putObject(STATUS_LISTENER_KEY, listener);
 		Environment environment = initializationContext.getEnvironment();
 		if (environment != null) {
 			getLoggerContext().putObject(ENVIRONMENT_KEY, environment);
@@ -226,21 +232,6 @@ public void initialize(LoggingInitializationContext initializationContext, Strin
 		markAsInitialized(loggerContext);
 	}
 
-	/**
-	 * Reset the stream used by the fallback listener to the current system out. This
-	 * allows the fallback listener to work with any captured output streams in a similar
-	 * way to the {@code follow} attribute of the {@code Console} appender.
-	 * @param statusLogger the status logger to update
-	 */
-	private void resetFallbackListenerStream(StatusLogger statusLogger) {
-		try {
-			statusLogger.getFallbackListener().setStream(System.out);
-		}
-		catch (NoSuchMethodError ex) {
-			// Ignore for older versions of Log4J
-		}
-	}
-
 	@Override
 	protected void loadDefaults(LoggingInitializationContext initializationContext, LogFile logFile) {
 		String location = getPackagedConfigFile((logFile != null) ? "log4j2-file.xml" : "log4j2.xml");
@@ -454,6 +445,11 @@ public void cleanUp() {
 		super.cleanUp();
 		LoggerContext loggerContext = getLoggerContext();
 		markAsUninitialized(loggerContext);
+		StatusConsoleListener listener = (StatusConsoleListener) getLoggerContext().getObject(STATUS_LISTENER_KEY);
+		if (listener != null) {
+			StatusLogger.getLogger().removeListener(listener);
+			getLoggerContext().removeObject(STATUS_LISTENER_KEY);
+		}
 		loggerContext.getConfiguration().removeFilter(FILTER);
 		Log4J2LoggingSystem.propertySource.setEnvironment(null);
 		getLoggerContext().removeObject(ENVIRONMENT_KEY);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -41,6 +41,8 @@
 import org.apache.logging.log4j.core.config.plugins.util.PluginRegistry;
 import org.apache.logging.log4j.core.util.ShutdownCallbackRegistry;
 import org.apache.logging.log4j.jul.Log4jBridgeHandler;
+import org.apache.logging.log4j.status.StatusListener;
+import org.apache.logging.log4j.status.StatusLogger;
 import org.apache.logging.log4j.util.PropertiesUtil;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
@@ -469,6 +471,42 @@ void initializeAttachesEnvironmentToLoggerContext() {
 		assertThat(environment).isSameAs(this.environment);
 	}
 
+	@Test
+	void initializeRegisterStatusListenerAndAttachToLoggerContext() {
+		this.loggingSystem.beforeInitialize();
+		this.loggingSystem.initialize(this.initializationContext, null, null);
+		LoggerContext loggerContext = (LoggerContext) LogManager.getContext(false);
+		StatusListener statusListener = (StatusListener) loggerContext
+			.getObject(Log4J2LoggingSystem.STATUS_LISTENER_KEY);
+		assertThat(statusListener).isNotNull();
+		assertThat(StatusLogger.getLogger().getListeners()).contains(statusListener);
+	}
+
+	@Test
+	void statusListenerIsUpdatedUponReinitialization() {
+		this.loggingSystem.beforeInitialize();
+		this.loggingSystem.initialize(this.initializationContext, null, null);
+		// listener should be registered
+		LoggerContext loggerContext = (LoggerContext) LogManager.getContext(false);
+		StatusListener statusListener = (StatusListener) loggerContext
+			.getObject(Log4J2LoggingSystem.STATUS_LISTENER_KEY);
+		assertThat(statusListener).isNotNull();
+		assertThat(StatusLogger.getLogger().getListeners()).contains(statusListener);
+
+		this.loggingSystem.cleanUp();
+		// listener should be removed from context and StatusLogger
+		assertThat(StatusLogger.getLogger().getListeners()).doesNotContain(statusListener);
+		assertThat(loggerContext.getObject(Log4J2LoggingSystem.STATUS_LISTENER_KEY)).isNull();
+
+		// a new listener should be registered
+		this.loggingSystem.beforeInitialize();
+		this.loggingSystem.initialize(this.initializationContext, null, null);
+		StatusListener statusListener1 = (StatusListener) loggerContext
+			.getObject(Log4J2LoggingSystem.STATUS_LISTENER_KEY);
+		assertThat(statusListener1).isNotNull();
+		assertThat(StatusLogger.getLogger().getListeners()).contains(statusListener1).doesNotContain(statusListener);
+	}
+
 	@Test
 	void initializeAddsSpringEnvironmentPropertySource() {
 		this.environment.setProperty("spring", "boot");