spring ApplicationListener接口
spring的ApplicationListener接口只有一个方法
/** * Handle an application event. * @param event the event to respond to */ void onApplicationEvent(E event);
用户可以选择自己实现这个方法,来实现自己的监听事件。
再来看一下spring是什么时候调用这个接口的实现类的呢?
首先看一下AbstractApplicationContext这个类。这个类可以说是spring生命周期里面特别重要的一个类
看一下refresh()方法
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
可以看到当刷新是最后会调finishRefresh();
再到方法里面看一下
/** * Finish the refresh of this context, invoking the LifecycleProcessor's * onRefresh() method and publishing the * {@link org.springframework.context.event.ContextRefreshedEvent}. */ protected void finishRefresh() { // Initialize lifecycle processor for this context. initLifecycleProcessor(); // Propagate refresh to lifecycle processor first. getLifecycleProcessor().onRefresh(); // Publish the final event. publishEvent(new ContextRefreshedEvent(this)); // Participate in LiveBeansView MBean, if active. LiveBeansView.registerApplicationContext(this); }
里面会执行publishEvent()
/** * Publish the given event to all listeners. * @param event the event to publish (may be an {@link ApplicationEvent} * or a payload object to be turned into a {@link PayloadApplicationEvent}) * @param eventType the resolved event type, if known * @since 4.2 */ protected void publishEvent(Object event, ResolvableType eventType) { Assert.notNull(event, "Event must not be null"); if (logger.isTraceEnabled()) { logger.trace("Publishing event in " + getDisplayName() + ": " + event); } // Decorate event as an ApplicationEvent if necessary ApplicationEvent applicationEvent; if (event instanceof ApplicationEvent) { applicationEvent = (ApplicationEvent) event; } else { applicationEvent = new PayloadApplicationEvent<Object>(this, event); if (eventType == null) { eventType = ResolvableType.forClassWithGenerics(PayloadApplicationEvent.class, event.getClass()); } } // Multicast right now if possible - or lazily once the multicaster is initialized if (this.earlyApplicationEvents != null) { this.earlyApplicationEvents.add(applicationEvent); } else { getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType); } // Publish event via parent context as well... if (this.parent != null) { if (this.parent instanceof AbstractApplicationContext) { ((AbstractApplicationContext) this.parent).publishEvent(event, eventType); } else { this.parent.publishEvent(event); } } }
有一句关键代码
getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
再看multicastEvent()
在SimpleApplicationEventMulticaster类里面的multicastEvent()方法
public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @Override public void run() { invokeListener(listener, event); } }); } else { invokeListener(listener, event); } } }
会将event里面的所有listener取出来交给Executor执行
/** * 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); } }
至此,我们就看到了我们自己定义的实现类是怎么被执行的了
posted on 2018-11-16 14:34 liguangming 阅读(178) 评论(0) 编辑 收藏 举报