Spring事件监听机制源码解析

Spring事件监听器使用

1.Spring事件监听体系包括三个组件:事件、事件监听器,事件广播器。

事件:定义事件类型和事件源,需要继承ApplicationEvent。

package com.ybe.eventLisitener;
import org.springframework.context.ApplicationEvent;

public class OrderEvent extends ApplicationEvent {
    private String name;
    public OrderEvent(Object source,String name) {
        super(source);
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

事件监听器:用来监听某一类的事件,并且执行具体业务逻辑,需要实现ApplicationListener

接口或者需要用@ListenerEvent(T)注解。好比观察者模式中的观察者。

package com.ybe.eventLisitener;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

@Component
public class OrderEventListener implements ApplicationListener<OrderEvent> {
    @Override
    public void onApplicationEvent(OrderEvent event) {
        if(event.getName().equals("下订单")){
            System.out.println("下单已完成...");
        }
    }
}

package com.ybe.eventLisitener;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class OrderEventListenerByAnnotation  {

    @EventListener(OrderEvent.class)
    public void onApplicationEvent(OrderEvent event) {
        if(event.getName().equals("下订单")){
            System.out.println("下单已完成...");
        }
    }
}

事件多播器:负责广播通知所有监听器,所有的事件监听器都注册在了事件多播器中。好比观察者模式中的被观察者。Spring容器默认生成的是同步事件多播器。可以自定义事件多播器,定义为异步方式。

import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.core.task.SimpleAsyncTaskExecutor;
import org.springframework.stereotype.Component;

import java.util.Scanner;

@Configuration
@ComponentScan(value = "com.ybe")
public class Config {
    @Bean
    public ApplicationEventMulticaster applicationEventMulticaster(){
        SimpleApplicationEventMulticaster eventMulticaster = new SimpleApplicationEventMulticaster();
        eventMulticaster.setTaskExecutor(new SimpleAsyncTaskExecutor());
        return eventMulticaster;
    }
}

Spring事件源码分析

1.创建多播器

创建 AnnotationConfigApplicationContext 的过程中,会执行refresh()中的initApplicationEventMulticaster()方法。该方法先获取bean工厂,然后判断工厂是否包含了beanName 为 applicationEventMulticaster的bean。如果包含了,则获取该bean,赋值给applicationEventMulticaster 属性。如果没有,则创建一个 SimpleApplicationEventMulticaster 对象,并且赋值给 applicationEventMulticaster 。实现了源码如下:

/**
	 * Initialize the ApplicationEventMulticaster.
	 * Uses SimpleApplicationEventMulticaster if none defined in the context.
	 * @see org.springframework.context.event.SimpleApplicationEventMulticaster
	 */
protected void initApplicationEventMulticaster() {
		// 获取当前bean工厂,一般是DefaultListableBeanFactory
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		// 判断容器中是否存在bdName为applicationEventMulticaster的bd,
         //也就是说自定义的事件监听多路广播器,必须实现  ApplicationEventMulticaster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,则默认采用SimpleApplicationEventMulticaster
			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() + "]");
			}
		}
	}

2.注册监听器

监听器的注册有两种,通过实现 ApplicationListener接口或者添加@EventListener注解。

一.通过接口方式注册。实现接口 ApplicationListener


注册的逻辑实现在refresh()中的registerListeners()方法里面。第一步,先获取当前ApplicationContext中已经添加的 applicationListeners(SpringMVC源码中有用到),遍历添加到多播器中。第二步,获取实现了ApplicationListener接口的listenerBeanNames集合,添加至多播器中。第三步,判断是否有早期事件,如果有则发起广播。

protected void registerListeners() {
      // Register statically specified listeners first.
      // 遍历应用程序中存在的监听器集合,并将对应的监听器添加到监听器的多路广播器中
      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!
      // 从容器中获取所有实现了ApplicationListener接口的bd的bdName
      // 放入ApplicationListenerBeans集合中
      String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
      for (String listenerBeanName : listenerBeanNames) {
         getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
      }

      // Publish early application events now that we finally have a multicaster...
      // 此处先发布早期的监听器集合
      Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
      this.earlyApplicationEvents = null;
      if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
         for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
            getApplicationEventMulticaster().multicastEvent(earlyEvent);
         }
      }
   }

思考一下,上面的代码中第二步为啥添加的是listenerBeanName?

如果监听器是懒加载的话(即有@Lazy 注解)。那么在这个时候创建监听器显然是不对的,这个时候不能创建监听器。所以添加监听器到多播器的具体逻辑放在初始化具体的监听器之后。通过 BeanPostProcessor 的接口实现。具体的实现类是 ApplicationListenerDetector 。这个类是在 refreah()中prepareBeanFactory()方法中添加的。代码如下:

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		// Tell the internal bean factory to use the context's class loader etc.
		beanFactory.setBeanClassLoader(getClassLoader());
		if (!shouldIgnoreSpel) {
			beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
		}
		beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

		// Configure the bean factory with context callbacks.
		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
		beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
		beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
		beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
		beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationStartupAware.class);

		// BeanFactory interface not registered as resolvable type in a plain factory.
		// MessageSource registered (and found for autowiring) as a bean.
		beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
		beanFactory.registerResolvableDependency(ResourceLoader.class, this);
		beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
		beanFactory.registerResolvableDependency(ApplicationContext.class, this);

		// Register early post-processor for detecting inner beans as ApplicationListeners.
    	// 添加 监听器后置处理器,在初始化具体的实现了 ApplicationListener 接口的Bean之后,进行调用。调用的是
    	// postProcessAfterInitialization()方法。
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

		// Detect a LoadTimeWeaver and prepare for weaving, if found.
		if (!NativeDetector.inNativeImage() && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			// Set a temporary ClassLoader for type matching.
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}

		// Register default environment beans.
		if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
		}
		if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {
			beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());
		}
	}
二、通过注解的方式注册。@EventListener(T)。

在创建 AnnotationConfigApplicationContext 的构造方法中,会执行org.springframework.context.annotation.AnnotationConfigUtils#registerAnnotationConfigProcessors(org.springframework.beans.factory.support.BeanDefinitionRegistry, java.lang.Object) 方法。这个方法中会添加两个 beanDefs, 代码如下:

if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}

if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}

EventListenerMethodProcessor:事件监听器的BeanFactory后置处理器,在前期会创建 DefaultEventListenerFactory ,后期在创建好Bean之后,根据 EventListener 属性,调用DefaultEventListenerFactory创建具体的 ApplicationListenerMethodAdapter 。

DefaultEventListenerFactory:监听器的创建工厂,用来创建 ApplicationListenerMethodAdapter 。

EventListenerMethodProcessor 的类继承图如下:

在refreash的invokeBeanFactoryPostProcessors()中会调用 org.springframework.context.event.EventListenerMethodProcessor#postProcessBeanFactory方法,获取EventListenerFactory 类型的 Bean。代码如下:

@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		this.beanFactory = beanFactory;
		// 获取或创建 EventListenerFactory 类型的 Bean
		Map<String, EventListenerFactory> beans = beanFactory.getBeansOfType(EventListenerFactory.class, false, false);
		List<EventListenerFactory> factories = new ArrayList<>(beans.values());
		AnnotationAwareOrderComparator.sort(factories);
		this.eventListenerFactories = factories;
	}

在 org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons 方法中,创建完所有的单例Bean 之后,会遍历所有Bean是否实现了 SmartInitializingSingleton 接口。如果实现接口会执行该 Bean 的 afterSingletonsInstantiated() 方法。代码如下:

public void preInstantiateSingletons() throws BeansException {
		if (logger.isTraceEnabled()) {
			logger.trace("Pre-instantiating singletons in " + this);
		}

		// Iterate over a copy to allow for init methods which in turn register new bean definitions.
		// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
		// 将所有BeanDefinition的名字创建一个集合
		List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

		// Trigger initialization of all non-lazy singleton beans...
		// 触发所有非延迟加载单例bean的初始化,遍历集合的对象
		for (String beanName : beanNames) {
			// 合并父类BeanDefinition
 			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			// 条件判断,抽象,单例,非懒加载
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
				// 判断是否实现了FactoryBean接口
				if (isFactoryBean(beanName)) {
					// 根据&+beanName来获取具体的对象
					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
					// 进行类型转换
					if (bean instanceof FactoryBean) {
						FactoryBean<?> factory = (FactoryBean<?>) bean;
						// 判断这个FactoryBean是否希望立即初始化
						boolean isEagerInit;
						if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
							isEagerInit = AccessController.doPrivileged(
									(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
									getAccessControlContext());
						}
						else {
							isEagerInit = (factory instanceof SmartFactoryBean &&
									((SmartFactoryBean<?>) factory).isEagerInit());
						}
						//  如果希望急切的初始化,则通过beanName获取bean实例
						if (isEagerInit) {
							getBean(beanName);
						}
					}
				}
				else {
					// 如果beanName对应的bean不是FactoryBean,只是普通的bean,通过beanName获取bean实例
					getBean(beanName);
				}
			}
		}

		// Trigger post-initialization callback for all applicable beans...
		// 遍历beanNames,触发所有SmartInitializingSingleton的后初始化回调
		for (String beanName : beanNames) {
			// 获取beanName对应的bean实例
			Object singletonInstance = getSingleton(beanName);
			// 判断singletonInstance是否实现了SmartInitializingSingleton接口
			if (singletonInstance instanceof SmartInitializingSingleton) {
				// 类型转换
				SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				// 触发SmartInitializingSingleton实现类的afterSingletonsInstantiated方法
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
						smartSingleton.afterSingletonsInstantiated();
						return null;
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
			}
		}
	}

org.springframework.context.event.EventListenerMethodProcessor#afterSingletonsInstantiated 中会调用私有方法 processBean()进行 ApplicationEventAdatper 的创建。代码如下:

	/**
	 * 该方法拿到某个bean的名称和它的目标类,再这个范围上检测@EventListener注解方法,生成和注册 ApplicationListenerMethodAdapter 实例
	 * @param beanName
	 * @param targetType
	 */
	private void processBean(final String beanName, final Class<?> targetType) {
		if (!this.nonAnnotatedClasses.contains(targetType) &&
				AnnotationUtils.isCandidateClass(targetType, EventListener.class) &&
				!isSpringContainerClass(targetType)) {

			Map<Method, EventListener> annotatedMethods = null;
			try {
				// 检测当前类targetType上使用了注解@EventListener的方法
				annotatedMethods = MethodIntrospector.selectMethods(targetType,
						(MethodIntrospector.MetadataLookup<EventListener>) method ->
								AnnotatedElementUtils.findMergedAnnotation(method, EventListener.class));
			}
			catch (Throwable ex) {
				// An unresolvable type in a method signature, probably from a lazy bean - let's ignore it.
				if (logger.isDebugEnabled()) {
					logger.debug("Could not resolve methods for bean with name '" + beanName + "'", ex);
				}
			}

			if (CollectionUtils.isEmpty(annotatedMethods)) {
				// 如果当前类targetType中没有任何使用了注解@EventListener的方法,则将该类保存到缓存nonAnnotatedClasses,从而
				// 避免当前处理方法重入该类,避免二次处理
				this.nonAnnotatedClasses.add(targetType);
				if (logger.isTraceEnabled()) {
					logger.trace("No @EventListener annotations found on bean class: " + targetType.getName());
				}
			}
			else {
				// Non-empty set of methods
				// 如果当前类targetType中有些方法使用了注解@EventListener,那么根据方法上的信息对应的创建和注册ApplicationListener实例
				ConfigurableApplicationContext context = this.applicationContext;
				Assert.state(context != null, "No ApplicationContext set");
				// 此处使用了this.eventListenerFactories,这些EventListenerFactory是在该类postProcessBeanFactory方法调用时被记录的
				List<EventListenerFactory> factories = this.eventListenerFactories;
				Assert.state(factories != null, "EventListenerFactory List not initialized");
				for (Method method : annotatedMethods.keySet()) {
					for (EventListenerFactory factory : factories) {
						if (factory.supportsMethod(method)) {
							Method methodToUse = AopUtils.selectInvocableMethod(method, context.getType(beanName));
							// 如果当前EventListenerFactory支持处理该@EventListener注解的方法,则使用它创建 ApplicationListenerMethodAdapter
							ApplicationListener<?> applicationListener =
									factory.createApplicationListener(beanName, targetType, methodToUse);
							if (applicationListener instanceof ApplicationListenerMethodAdapter) {
								((ApplicationListenerMethodAdapter) applicationListener).init(context, this.evaluator);
							}
							// 将创建的ApplicationListener加入到容器中
							context.addApplicationListener(applicationListener);
							break;
						}
					}
				}
				if (logger.isDebugEnabled()) {
					logger.debug(annotatedMethods.size() + " @EventListener methods processed on bean '" +
							beanName + "': " + annotatedMethods);
				}
			}
		}
	}

3.多播器广播事件

可以通过调用 org.springframework.context.support.AbstractApplicationContext#publishEvent(java.lang.Object, org.springframework.core.ResolvableType) 方法进行事件的调用。代码如下:

/**
	 * 将给定事件发布到所有监听器
	 */
	protected void publishEvent(Object event, @Nullable ResolvableType eventType) {
		// 如果event为null,抛出异常
		Assert.notNull(event, "Event must not be null");

		// Decorate event as an ApplicationEvent if necessary
		// 装饰事件作为一个应用事件,如果有必要
		ApplicationEvent applicationEvent;
		// 如果event是ApplicationEvent的实例
		if (event instanceof ApplicationEvent) {
			// 将event强转为ApplicationEvent对象
			applicationEvent = (ApplicationEvent) event;
		}
		else {
			// PayloadApplicationEvent:携带任意有效负载的ApplicationEvent。
			// 创建一个新的PayloadApplicationEvent
			applicationEvent = new PayloadApplicationEvent<>(this, event);
			// 如果eventType为 null
			if (eventType == null) {
				// 将applicationEvent转换为PayloadApplicationEvent 象,引用其ResolvableType对象
				eventType = ((PayloadApplicationEvent<?>) applicationEvent).getResolvableType();
			}
		}

		// Multicast right now if possible - or lazily once the multicaster is initialized
		// 如果可能的话,现在就进行组播——或者在组播初始化后延迟
		// earlyApplicationEvents:在多播程序设置之前发布的ApplicationEvent
		// 如果earlyApplicationEvents不为 null,这种情况只在上下文的多播器还没有初始化的情况下才会成立,会将applicationEvent
		// 添加到earlyApplicationEvents保存起来,待多博器初始化后才继续进行多播到适当的监听器
		if (this.earlyApplicationEvents != null) {
			//将applicationEvent添加到 earlyApplicationEvents
			this.earlyApplicationEvents.add(applicationEvent);
		}
		else {
			// 多播applicationEvent到适当的监听器
			getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
		}

		// Publish event via parent context as well...
		// 通过父上下文发布事件
		// 如果parent不为null
		if (this.parent != null) {
			// 如果parent是AbstractApplicationContext的实例
			if (this.parent instanceof AbstractApplicationContext) {
				// 将event多播到所有适合的监听器。如果event不是ApplicationEvent实例,会将其封装成PayloadApplicationEvent对象再进行多播
				((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
			}
			else {
				// 通知与event事件应用程序注册的所有匹配的监听器
				this.parent.publishEvent(event);
			}
		}
	}

SimpleApplicationEventMulticaster 中的 multicasEvent,invokeListener,doInvokeListener 三个方法代码如下:

/**
	 * 将给定事件发布到所有监听器
	 */
	protected void publishEvent(Object event, @Nullable ResolvableType eventType) {
		// 如果event为null,抛出异常
		Assert.notNull(event, "Event must not be null");

		// Decorate event as an ApplicationEvent if necessary
		// 装饰事件作为一个应用事件,如果有必要
		ApplicationEvent applicationEvent;
		// 如果event是ApplicationEvent的实例
		if (event instanceof ApplicationEvent) {
			// 将event强转为ApplicationEvent对象
			applicationEvent = (ApplicationEvent) event;
		}
		else {
			// PayloadApplicationEvent:携带任意有效负载的ApplicationEvent。
			// 创建一个新的PayloadApplicationEvent
			applicationEvent = new PayloadApplicationEvent<>(this, event);
			// 如果eventType为 null
			if (eventType == null) {
				// 将applicationEvent转换为PayloadApplicationEvent 象,引用其ResolvableType对象
				eventType = ((PayloadApplicationEvent<?>) applicationEvent).getResolvableType();
			}
		}

		// Multicast right now if possible - or lazily once the multicaster is initialized
		// 如果可能的话,现在就进行组播——或者在组播初始化后延迟
		// earlyApplicationEvents:在多播程序设置之前发布的ApplicationEvent
		// 如果earlyApplicationEvents不为 null,这种情况只在上下文的多播器还没有初始化的情况下才会成立,会将applicationEvent
		// 添加到earlyApplicationEvents保存起来,待多博器初始化后才继续进行多播到适当的监听器
		if (this.earlyApplicationEvents != null) {
			//将applicationEvent添加到 earlyApplicationEvents
			this.earlyApplicationEvents.add(applicationEvent);
		}
		else {
			// 多播applicationEvent到适当的监听器
			getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
		}

		// Publish event via parent context as well...
		// 通过父上下文发布事件
		// 如果parent不为null
		if (this.parent != null) {
			// 如果parent是AbstractApplicationContext的实例
			if (this.parent instanceof AbstractApplicationContext) {
				// 将event多播到所有适合的监听器。如果event不是ApplicationEvent实例,会将其封装成PayloadApplicationEvent对象再进行多播
				((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
			}
			else {
				// 通知与event事件应用程序注册的所有匹配的监听器
				this.parent.publishEvent(event);
			}
		}
	}
	protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
		// 获取此多播器的当前错误处理程序
		ErrorHandler errorHandler = getErrorHandler();
		// 如果errorHandler不为null
		if (errorHandler != null) {
			try {
				// 回调listener的onApplicationEvent方法,传入event
				doInvokeListener(listener, event);
			}
			catch (Throwable err) {
				// 交给errorHandler接收处理err
				errorHandler.handleError(err);
			}
		}
		else {
			// 回调listener的onApplicationEvent方法,传入event
			doInvokeListener(listener, event);
		}
	}
	/**
	 * 回调listener的onApplicationEvent方法,传入 event
	 * @param listener
	 * @param event
	 */
	@SuppressWarnings({"rawtypes", "unchecked"})
	private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
		try {
			//回调listener的onApplicationEvent方法,传入	        			event:contextrefreshListener:onapplicaitonEvent:FrameworkServlet.this.onApplicationEvent()
			listener.onApplicationEvent(event);
		}
		catch (ClassCastException ex) {
			//获取异常信息
			String msg = ex.getMessage();
			if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
				// 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.isTraceEnabled()) {
					logger.trace("Non-matching event type for listener: " + listener, ex);
				}
			}
			else {
				//抛出异常
				throw ex;
			}
		}
	}

SpringMVC中事件使用

SpringMVC中就是通过Spring的事件机制进行九大组件的初始化。

1.ContextRefreshListener监听器的定义

监听器定义在FrameworkServlet类中,作为内部类。代码如下:

	private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {

		@Override
		public void onApplicationEvent(ContextRefreshedEvent event) {
			FrameworkServlet.this.onApplicationEvent(event);
		}
	}

监听器的添加在org.springframework.web.servlet.FrameworkServlet#configureAndRefreshWebApplicationContext 中进行。通过SourceFilteringListener进行包装。添加代码如下:

	// 添加监听器sourceFilteringListener到wac中,实际监听的是ContextRefreshListener所监听的事件,监听ContextRefreshedEvent事件,
		// 当接收到消息之后会调用onApplicationEvent方法,调用onRefresh方法,并将refreshEventReceived标志设置为true,表示已经refresh过
		wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));

2.多播器添加已经定义的ContextRefreshListener事件监听器

在refresh中的registerListeners方法进行添加,代码如下:

		// Register statically specified listeners first.
		// 遍历应用程序中存在的监听器集合,并将对应的监听器添加到监听器的多路广播器中
		for (ApplicationListener<?> listener : getApplicationListeners()) {
			getApplicationEventMulticaster().addApplicationListener(listener);
		}

3.ContextRefreshListener事件监听器的触发

在refresh中的finishRefresh()方法中,会调用publishEvnet(new ContextRefreshedEvent(this))发布事件。进行多播器广播,代码如下

// 多播applicationEvent到适当的监听器
getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);

最终会调到FrameworkServlet.this.onApplicationEvent(event)。

	public void onApplicationEvent(ContextRefreshedEvent event) {
		// 标记 refreshEventReceived 为true
		this.refreshEventReceived = true;
		synchronized (this.onRefreshMonitor) {
			// 处理事件中的 ApplicationContext 对象,空实现,子类DispatcherServlet会实现
			onRefresh(event.getApplicationContext());
		}
	}
@Override
	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}
protected void initStrategies(ApplicationContext context) {
		// 初始化 MultipartResolver:主要用来处理文件上传.如果定义过当前类型的bean对象,那么直接获取,如果没有的话,可以为null
		initMultipartResolver(context);
		// 初始化 LocaleResolver:主要用来处理国际化配置,基于URL参数的配置(AcceptHeaderLocaleResolver),基于session的配置(SessionLocaleResolver),基于cookie的配置(CookieLocaleResolver)
		initLocaleResolver(context);
		// 初始化 ThemeResolver:主要用来设置主题Theme
		initThemeResolver(context);
		// 初始化 HandlerMapping:映射器,用来将对应的request跟controller进行对应
		initHandlerMappings(context);
		// 初始化 HandlerAdapter:处理适配器,主要包含Http请求处理器适配器,简单控制器处理器适配器,注解方法处理器适配器
		initHandlerAdapters(context);
		// 初始化 HandlerExceptionResolver:基于HandlerExceptionResolver接口的异常处理
		initHandlerExceptionResolvers(context);
		// 初始化 RequestToViewNameTranslator:当controller处理器方法没有返回一个View对象或逻辑视图名称,并且在该方法中没有直接往response的输出流里面写数据的时候,spring将会采用约定好的方式提供一个逻辑视图名称
		initRequestToViewNameTranslator(context);
		// 初始化 ViewResolver: 将ModelAndView选择合适的视图进行渲染的处理器
		initViewResolvers(context);
		// 初始化 FlashMapManager: 提供请求存储属性,可供其他请求使用
		initFlashMapManager(context);
	}

 1 total views,  1 views today

页面下部广告