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.sp
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
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;
}
}
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() + "]");
}
}
}
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());
}
}
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);
}
}
}
}
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()));
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);
}
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);
}