SimpleApplicationEventMulticaster supports a configurable ErrorHandler strategy

Issue: SPR-11551

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

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2014 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.
@@ -21,6 +21,7 @@ import java.util.concurrent.Executor;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
+import org.springframework.util.ErrorHandler;
 
 /**
  * Simple implementation of the {@link ApplicationEventMulticaster} interface.
@@ -32,7 +33,7 @@ import org.springframework.context.ApplicationListener;
  *
  * <p>By default, all listeners are invoked in the calling thread.
  * This allows the danger of a rogue listener blocking the entire application,
- * but adds minimal overhead. Specify an alternative TaskExecutor to have
+ * but adds minimal overhead. Specify an alternative task executor to have
  * listeners executed in different threads, for example from a thread pool.
  *
  * @author Rod Johnson
@@ -43,6 +44,8 @@ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventM
 
 	private Executor taskExecutor;
 
+	private ErrorHandler errorHandler;
+
 
 	/**
 	 * Create a new SimpleApplicationEventMulticaster.
@@ -59,10 +62,11 @@ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventM
 
 
 	/**
-	 * Set the TaskExecutor to execute application listeners with.
-	 * <p>Default is a SyncTaskExecutor, executing the listeners synchronously
-	 * in the calling thread.
-	 * <p>Consider specifying an asynchronous TaskExecutor here to not block the
+	 * Set a custom executor (typically a {@link org.springframework.core.task.TaskExecutor})
+	 * to invoke each listener with.
+	 * <p>Default is equivalent to {@link org.springframework.core.task.SyncTaskExecutor},
+	 * executing all listeners synchronously in the calling thread.
+	 * <p>Consider specifying an asynchronous task executor here to not block the
 	 * caller until all listeners have been executed. However, note that asynchronous
 	 * execution will not participate in the caller's thread context (class loader,
 	 * transaction association) unless the TaskExecutor explicitly supports this.
@@ -74,29 +78,77 @@ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventM
 	}
 
 	/**
-	 * Return the current TaskExecutor for this multicaster.
+	 * Return the current task executor for this multicaster.
 	 */
 	protected Executor getTaskExecutor() {
 		return this.taskExecutor;
 	}
 
+	/**
+	 * Set the {@link ErrorHandler} to invoke in case of an exception thrown
+	 * from a listener.
+	 * <p>Default is none, with a listener exception stopping the current
+	 * multicast and getting propagated to the publisher of the current event.
+	 * In case of a {@link #setTaskExecutor task executor} specified, each
+	 * individual listener exception will get propagated to the executor but
+	 * won't necessarily stop execution of other listeners.
+	 * <p>Consider setting an {@link ErrorHandler} implementation that catches
+	 * and logs exceptions (a la
+	 * {@link org.springframework.scheduling.support.TaskUtils#LOG_AND_SUPPRESS_ERROR_HANDLER})
+	 * or an implementation that logs exceptions while nevertheless propagating them
+	 * ({@link org.springframework.scheduling.support.TaskUtils#LOG_AND_PROPAGATE_ERROR_HANDLER}).
+	 * @since 4.1
+	 */
+	public void setErrorHandler(ErrorHandler errorHandler) {
+		this.errorHandler = errorHandler;
+	}
+
+	/**
+	 * Return the current error handler for this multicaster.
+	 * @since 4.1
+	 */
+	protected ErrorHandler getErrorHandler() {
+		return this.errorHandler;
+	}
+
 
 	@Override
-	@SuppressWarnings({ "unchecked", "rawtypes" })
 	public void multicastEvent(final ApplicationEvent event) {
-		for (final ApplicationListener listener : getApplicationListeners(event)) {
+		for (final ApplicationListener<?> listener : getApplicationListeners(event)) {
 			Executor executor = getTaskExecutor();
 			if (executor != null) {
 				executor.execute(new Runnable() {
 					@Override
 					public void run() {
-						listener.onApplicationEvent(event);
+						invokeListener(listener, event);
 					}
 				});
 			}
 			else {
+				invokeListener(listener, event);
+			}
+		}
+	}
+
+	/**
+	 * Invoke the given listener with the given event.
+	 * @param listener the ApplicationListener to invoke
+	 * @param event the current event to propagate
+	 * @since 4.1
+	 */
+	@SuppressWarnings({"unchecked", "rawtypes"})
+	protected void invokeListener(ApplicationListener listener, ApplicationEvent event) {
+		ErrorHandler errorHandler = getErrorHandler();
+		if (errorHandler != null) {
+			try {
 				listener.onApplicationEvent(event);
 			}
+			catch (Throwable err) {
+				errorHandler.handleError(err);
+			}
+		}
+		else {
+			listener.onApplicationEvent(event);
 		}
 	}
 

spring-context/src/test/java/org/springframework/context/event/ApplicationContextEventTests.java

@@ -18,6 +18,7 @@ package org.springframework.context.event;
 
 import java.util.HashSet;
 import java.util.Set;
+import java.util.concurrent.Executor;
 
 import org.aopalliance.intercept.MethodInvocation;
 import org.junit.Test;
@@ -33,6 +34,7 @@ import org.springframework.context.BeanThatListens;
 import org.springframework.context.support.AbstractApplicationContext;
 import org.springframework.context.support.StaticApplicationContext;
 import org.springframework.core.Ordered;
+import org.springframework.scheduling.support.TaskUtils;
 import org.springframework.tests.sample.beans.TestBean;
 
 import static org.junit.Assert.*;
@@ -59,6 +61,60 @@ public class ApplicationContextEventTests {
 		verify(listener).onApplicationEvent(evt);
 	}
 
+	@Test
+	public void simpleApplicationEventMulticasterWithTaskExecutor() {
+		@SuppressWarnings("unchecked")
+		ApplicationListener<ApplicationEvent> listener = mock(ApplicationListener.class);
+		ApplicationEvent evt = new ContextClosedEvent(new StaticApplicationContext());
+
+		SimpleApplicationEventMulticaster smc = new SimpleApplicationEventMulticaster();
+		smc.setTaskExecutor(new Executor() {
+			@Override
+			public void execute(Runnable command) {
+				command.run();
+				command.run();
+			}
+		});
+		smc.addApplicationListener(listener);
+
+		smc.multicastEvent(evt);
+		verify(listener, times(2)).onApplicationEvent(evt);
+	}
+
+	@Test
+	public void simpleApplicationEventMulticasterWithException() {
+		@SuppressWarnings("unchecked")
+		ApplicationListener<ApplicationEvent> listener = mock(ApplicationListener.class);
+		ApplicationEvent evt = new ContextClosedEvent(new StaticApplicationContext());
+
+		SimpleApplicationEventMulticaster smc = new SimpleApplicationEventMulticaster();
+		smc.addApplicationListener(listener);
+
+		RuntimeException thrown = new RuntimeException();
+		doThrow(thrown).when(listener).onApplicationEvent(evt);
+		try {
+			smc.multicastEvent(evt);
+			fail("Should have thrown RuntimeException");
+		}
+		catch (RuntimeException ex) {
+			assertSame(thrown, ex);
+		}
+	}
+
+	@Test
+	public void simpleApplicationEventMulticasterWithErrorHandler() {
+		@SuppressWarnings("unchecked")
+		ApplicationListener<ApplicationEvent> listener = mock(ApplicationListener.class);
+		ApplicationEvent evt = new ContextClosedEvent(new StaticApplicationContext());
+
+		SimpleApplicationEventMulticaster smc = new SimpleApplicationEventMulticaster();
+		smc.setErrorHandler(TaskUtils.LOG_AND_SUPPRESS_ERROR_HANDLER);
+		smc.addApplicationListener(listener);
+
+		doThrow(new RuntimeException()).when(listener).onApplicationEvent(evt);
+		smc.multicastEvent(evt);
+	}
+
 	@Test
 	public void orderedListeners() {
 		MyOrderedListener1 listener1 = new MyOrderedListener1();