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initApplicationEventMulticaster源码解析

初始化事件监听多路广播器

/**	 * Initialize the ApplicationEventMulticaster.	 * Uses SimpleApplicationEventMulticaster if none defined in the context.	 * @see org.springframework.context.event.SimpleApplicationEventMulticaster	 */	protected void initApplicationEventMulticaster() {   		//获取Bean工厂，一般为DefaultListBeanFactory		ConfigurableListableBeanFactory beanFactory = getBeanFactory();		//首先判断是否已有xml文件定义了id为aplicationEventMulticaster的bean对象		//自定义的事件监听多路广播器需要实现AplicationEventMulticaster接口		if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {   			//如果有，则从Bean工厂得到这个bean对象			this.applicationEventMulticaster =					beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);			if (logger.isTraceEnabled()) {   				logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");			}		}		else {   			//如果没有xml文件定义这个bean对象，那么新建一个SimpleApplicationEventMulticaster类作为aplicationEventMulticaster的Bean			//因为SimpleApplicationEventMulticaster继承了AbstractApplicationEventMulticaster抽象类，而这个抽象类实现了aplicationEventMulticaster接口			//因此SimpleApplicationEventMulticaster是aplicationEventMulticaster接口的一个实现			this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);			beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);			if (logger.isTraceEnabled()) {   				logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +						"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");			}		}	}

事件的执行主要是在Bean初始化之后；就是publishEvent方法

protected void finishRefresh() {   		// Clear context-level resource caches (such as ASM metadata from scanning).		//清除缓存尤其是扫描过程中像ASM的数据		clearResourceCaches();		// Initialize lifecycle processor for this context.		//为上下文初始化生命周期处理器		initLifecycleProcessor();		// Propagate refresh to lifecycle processor first.		//首先传播刷新生命周期处理器		getLifecycleProcessor().onRefresh();		// Publish the final event.		//发布事件		publishEvent(new ContextRefreshedEvent(this));		// Participate in LiveBeansView MBean, if active.		LiveBeansView.registerApplicationContext(this);	}

/**	 * 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, @Nullable ResolvableType eventType) {   		Assert.notNull(event, "Event must not be null");		// Decorate event as an ApplicationEvent if necessary		//如有必要，将事件装饰为ApplicationEvent		ApplicationEvent applicationEvent;		if (event instanceof ApplicationEvent) {   			applicationEvent = (ApplicationEvent) event;		}		else {   			//不是事件就转为事件			applicationEvent = new PayloadApplicationEvent<>(this, event);			if (eventType == null) {   				eventType = ((PayloadApplicationEvent<?>) applicationEvent).getResolvableType();			}		}		// Multicast right now if possible - or lazily once the multicaster is initialized		//如果可能，立即进行多播-或一旦初始化多播器就懒惰		if (this.earlyApplicationEvents != null) {   			this.earlyApplicationEvents.add(applicationEvent);		}		else {   			//获取事件广播器，发布事件			getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);		}		// Publish event via parent context as well...		//如果存在父容器，那么父容器也发布事件		if (this.parent != null) {   			if (this.parent instanceof AbstractApplicationContext) {   				((AbstractApplicationContext) this.parent).publishEvent(event, eventType);			}			else {   				this.parent.publishEvent(event);			}		}	}

具体的发布逻辑在multicastEvent方法中

@Override	public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {   		ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));		Executor executor = getTaskExecutor();		//遍历所有监听器		for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {   			if (executor != null) {   			//执行监听器的方法				executor.execute(() -> invokeListener(listener, event));			}			else {   				invokeListener(listener, event);			}		}	}

这个逻辑也很简单，无非就是启动一个线程池，去调用这些监听器的处理这些事件的方法