Run listener/send task locally as fallback on RejectedExecutionException

Closes gh-32171

spring-context/src/main/java/org/springframework/context/event/SimpleApplicationEventMulticaster.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -17,6 +17,7 @@
 package org.springframework.context.event;
 
 import java.util.concurrent.Executor;
+import java.util.concurrent.RejectedExecutionException;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -143,7 +144,13 @@ public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType even
 		Executor executor = getTaskExecutor();
 		for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
 			if (executor != null && listener.supportsAsyncExecution()) {
-				executor.execute(() -> invokeListener(listener, event));
+				try {
+					executor.execute(() -> invokeListener(listener, event));
+				}
+				catch (RejectedExecutionException ex) {
+					// Probably on shutdown -> invoke listener locally instead
+					invokeListener(listener, event);
+				}
 			}
 			else {
 				invokeListener(listener, event);

spring-messaging/src/main/java/org/springframework/messaging/support/ExecutorSubscribableChannel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -19,6 +19,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Executor;
+import java.util.concurrent.RejectedExecutionException;
 
 import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
@@ -96,11 +97,18 @@ private void updateExecutorInterceptorsFor(ChannelInterceptor interceptor) {
 	public boolean sendInternal(Message<?> message, long timeout) {
 		for (MessageHandler handler : getSubscribers()) {
 			SendTask sendTask = new SendTask(message, handler);
-			if (this.executor == null) {
-				sendTask.run();
+			if (this.executor != null) {
+				try {
+					this.executor.execute(sendTask);
+				}
+				catch (RejectedExecutionException ex) {
+					// Probably on shutdown -> run send task locally instead
+					sendTask.run();
+				}
 			}
 			else {
-				this.executor.execute(sendTask);
+				// No executor configured -> always run send tasks locally
+				sendTask.run();
 			}
 		}
 		return true;