Java tutorial
/* * Copyright 2002-2018 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. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.context.event; import java.util.concurrent.Executor; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.beans.factory.BeanFactory; import org.springframework.context.ApplicationEvent; import org.springframework.context.ApplicationListener; import org.springframework.core.ResolvableType; import org.springframework.lang.Nullable; import org.springframework.util.ErrorHandler; /** * Simple implementation of the {@link ApplicationEventMulticaster} interface. * * <p>Multicasts all events to all registered listeners, leaving it up to * the listeners to ignore events that they are not interested in. * Listeners will usually perform corresponding {@code instanceof} * checks on the passed-in event object. * * <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 task executor to have * listeners executed in different threads, for example from a thread pool. * * @author Rod Johnson * @author Juergen Hoeller * @author Stephane Nicoll * @see #setTaskExecutor */ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventMulticaster { @Nullable private Executor taskExecutor; @Nullable private ErrorHandler errorHandler; /** * Create a new SimpleApplicationEventMulticaster. */ public SimpleApplicationEventMulticaster() { } /** * Create a new SimpleApplicationEventMulticaster for the given BeanFactory. */ public SimpleApplicationEventMulticaster(BeanFactory beanFactory) { setBeanFactory(beanFactory); } /** * 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. * @see org.springframework.core.task.SyncTaskExecutor * @see org.springframework.core.task.SimpleAsyncTaskExecutor */ public void setTaskExecutor(@Nullable Executor taskExecutor) { this.taskExecutor = taskExecutor; } /** * Return the current task executor for this multicaster. */ @Nullable protected Executor getTaskExecutor() { return this.taskExecutor; } /** * Set the {@link ErrorHandler} to invoke in case an exception is 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. * If a {@linkplain #setTaskExecutor task executor} is 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 * (e.g. {@link org.springframework.scheduling.support.TaskUtils#LOG_AND_PROPAGATE_ERROR_HANDLER}). * @since 4.1 */ public void setErrorHandler(@Nullable ErrorHandler errorHandler) { this.errorHandler = errorHandler; } /** * Return the current error handler for this multicaster. * @since 4.1 */ @Nullable protected ErrorHandler getErrorHandler() { return this.errorHandler; } @Override public void multicastEvent(ApplicationEvent event) { multicastEvent(event, resolveDefaultEventType(event)); } @Override public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(() -> invokeListener(listener, event)); } else { invokeListener(listener, event); } } } private ResolvableType resolveDefaultEventType(ApplicationEvent event) { return ResolvableType.forInstance(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 */ protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) { ErrorHandler errorHandler = getErrorHandler(); if (errorHandler != null) { try { doInvokeListener(listener, event); } catch (Throwable err) { errorHandler.handleError(err); } } else { doInvokeListener(listener, event); } } @SuppressWarnings({ "unchecked", "rawtypes" }) private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) { try { listener.onApplicationEvent(event); } catch (ClassCastException ex) { String msg = ex.getMessage(); if (msg == null || matchesClassCastMessage(msg, event.getClass().getName())) { // Possibly a lambda-defined listener which we could not resolve the generic event type for // -> let's suppress the exception and just log a debug message. Log logger = LogFactory.getLog(getClass()); if (logger.isDebugEnabled()) { logger.debug("Non-matching event type for listener: " + listener, ex); } } else { throw ex; } } } private boolean matchesClassCastMessage(String classCastMessage, String eventClassName) { // On Java 8, the message simply starts with the class name: "java.lang.String cannot be cast..." if (classCastMessage.startsWith(eventClassName)) { return true; } // On Java 9, the message contains the module name: "java.base/java.lang.String cannot be cast..." int moduleSeparatorIndex = classCastMessage.indexOf('/'); if (moduleSeparatorIndex != -1 && classCastMessage.startsWith(eventClassName, moduleSeparatorIndex + 1)) { return true; } // Assuming an unrelated class cast failure... return false; } }