Spring事件
Spring事件体系包括三个组件:事件,事件监听器,事件广播器
事件:ApplicationEvent
事件监听器:ApplicationListener,对监听到的事件进行处理。
事件广播器:ApplicationEventMulticaster,将Springpublish的事件广播给所有的监听器。
Spring在ApplicationContext接口的抽象实现类AbstractApplicationContext中完成了事件体系的搭建。
AbstractApplicationContext拥有一个applicationEventMulticaster成员变 量,applicationEventMulticaster提供了容器监听器的注册表。
AbstractApplicationContext在refresh()这个容器启动方法中搭建了事件的基础设施。
refresh
1、事件广播器的初始化:
1 public void refresh() throws BeansException, IllegalStateException { 2 synchronized (this.startupShutdownMonitor) { 3 // Prepare this context for refreshing. 4 prepareRefresh(); 5 6 // Tell the subclass to refresh the internal bean factory. 7 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); 8 9 // Prepare the bean factory for use in this context. 10 prepareBeanFactory(beanFactory); 11 12 try { 13 // Allows post-processing of the bean factory in context subclasses. 14 postProcessBeanFactory(beanFactory); 15 16 // Invoke factory processors registered as beans in the context. 17 invokeBeanFactoryPostProcessors(beanFactory); 18 19 // Register bean processors that intercept bean creation. 20 registerBeanPostProcessors(beanFactory); 21 22 // Initialize message source for this context. 23 initMessageSource(); 24 25 // Initialize event multicaster for this context. 26 initApplicationEventMulticaster(); 27 28 // Initialize other special beans in specific context subclasses. 29 onRefresh(); 30 31 // Check for listener beans and register them. 32 registerListeners(); 33 34 // Instantiate all remaining (non-lazy-init) singletons. 35 finishBeanFactoryInitialization(beanFactory); 36 37 // Last step: publish corresponding event. 38 finishRefresh(); 39 } 40 41 catch (BeansException ex) { 42 // Destroy already created singletons to avoid dangling resources. 43 destroyBeans(); 44 45 // Reset 'active' flag. 46 cancelRefresh(ex); 47 48 // Propagate exception to caller. 49 throw ex; 50 } 51 } 52 }
View Code
/** * Initialize the ApplicationEventMulticaster. * Uses SimpleApplicationEventMulticaster if none defined in the context. * @see org.springframework.context.event.SimpleApplicationEventMulticaster */ protected void initApplicationEventMulticaster() { ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) { this.applicationEventMulticaster = beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class); if (logger.isDebugEnabled()) { logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]"); } } else { this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory); beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster); if (logger.isDebugEnabled()) { logger.debug("Unable to locate ApplicationEventMulticaster with name '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "': using default [" + this.applicationEventMulticaster + "]"); } } }
用户可以在配置文件中为容器定义一个自定义的事件广播器,只要实现ApplicationEventMulticaster就可以了,Spring会通过 反射的机制将其注册成容器的事件广播器,如果没有找到配置的外部事件广播器,Spring自动使用 SimpleApplicationEventMulticaster作为事件广播器。
2、注册事件监听器
View Code
/** * Add beans that implement ApplicationListener as listeners. * Doesn't affect other listeners, which can be added without being beans. */ protected void registerListeners() { // Register statically specified listeners first. for (ApplicationListener<?> listener : getApplicationListeners()) { getApplicationEventMulticaster().addApplicationListener(listener); } // Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let post-processors apply to them! String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false); for (String lisName : listenerBeanNames) { getApplicationEventMulticaster().addApplicationListenerBean(lisName); } }
Spring根据反射机制,使用ListableBeanFactory的getBeansOfType方法,从BeanDefinitionRegistry中找出所有实现 org.springframework.context.ApplicationListener的Bean,将它们注册为容器的事件监听器,实际的操作就是将其添加到事件广播器所提供的监听器注册表中。
3、发布事件
View Code
/** * Publish the given event to all listeners. * <p>Note: Listeners get initialized after the MessageSource, to be able * to access it within listener implementations. Thus, MessageSource * implementations cannot publish events. * @param event the event to publish (may be application-specific or a * standard framework event) */ public void publishEvent(ApplicationEvent event) { Assert.notNull(event, "Event must not be null"); if (logger.isTraceEnabled()) { logger.trace("Publishing event in " + getDisplayName() + ": " + event); } getApplicationEventMulticaster().multicastEvent(event); if (this.parent != null) { this.parent.publishEvent(event); } }
在AbstractApplicationContext的publishEvent方法中, Spring委托ApplicationEventMulticaster将事件通知给所有的事件监听器
4、Spring默认的事件广播器SimpleApplicationEventMulticaster
View Code
@SuppressWarnings("unchecked") public void multicastEvent(final ApplicationEvent event) { for (final ApplicationListener listener : getApplicationListeners(event)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @SuppressWarnings("unchecked") public void run() { listener.onApplicationEvent(event); } }); } else { listener.onApplicationEvent(event); } } }
遍历注册的每个监听器,并启动来调用每个监听器的onApplicationEvent方法。