1、Spring事件监听器使用

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

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。下面分别有两种实现

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

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。即这个事件多播器可以不定义，直接用默认的就行。也可以自定义执行相关需要的逻辑

import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.core.task.SimpleAsyncTaskExecutor;
import org.springframework.stereotype.Component;
@Configuration
@ComponentScan(value = "com.ybe")
public class Config {@Beanpublic ApplicationEventMulticaster applicationEventMulticaster(){SimpleApplicationEventMulticaster eventMulticaster = new SimpleApplicationEventMulticaster();eventMulticaster.setTaskExecutor(new SimpleAsyncTaskExecutor());// todoreturn eventMulticaster;}
}

2、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DefaultListableBeanFactoryConfigurableListableBeanFactory 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SimpleApplicationEventMulticasterthis.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，springboot的run启动流程源码中有用到），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);}}}

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：

@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {this.beanFactory = beanFactory;// 获取或创建 EventListenerFactory 类型的 BeanMap<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BeanDefinitionRootBeanDefinition 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 ApplicationListenerMethodAdapterApplicationListener<?> 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PayloadApplicationEventapplicationEvent = new PayloadApplicationEvent<>(this, event);// 如果eventType为 nullif (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 earlyApplicationEventsthis.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nullif (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PayloadApplicationEventapplicationEvent = new PayloadApplicationEvent<>(this, event);// 如果eventType为 nullif (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 earlyApplicationEventsthis.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nullif (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nullif (errorHandler != null) {try {// 回调listener的onApplicationEvent方法，传入eventdoInvokeListener(listener, event);}catch (Throwable err) {// 交给errorHandler接收处理errerrorHandler.handleError(err);}}else {// 回调listener的onApplicationEvent方法，传入eventdoInvokeListener(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;}}}

3、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> {@Overridepublic 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truethis.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());}}

@Overrideprotected 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nullinitMultipartResolver(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ThemeinitThemeResolver(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);}