Spring Boot2 源码 run getRunListeners方法（二）

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1.spring boot2 源码 SpringApplication构造方法

SpringApplication继续run方法查看源码

public ConfigurableApplicationContext run(String... args) {// 1、创建并启动计时监控类StopWatch stopWatch = new StopWatch();stopWatch.start();// 2、初始化应用上下文和异常报告集合ConfigurableApplicationContext context = null;Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();// 3、设置系统属性 `java.awt.headless` 的值，默认值为：trueconfigureHeadlessProperty();// 4、创建所有 Spring 运行监听器并发布应用启动事件SpringApplicationRunListeners listeners = getRunListeners(args);//4.1启动各个SpringApplicationRunListener 监听器实例(EventPublishingRunListener) listeners.starting();try {// 5、初始化默认应用参数类ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);// 6、根据运行监听器和应用参数来准备 Spring 环境ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);configureIgnoreBeanInfo(environment);// 7、创建 Banner 打印类Banner printedBanner = printBanner(environment);// 8、创建应用上下文context = createApplicationContext();// 9、准备异常报告器exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,new Class[] { ConfigurableApplicationContext.class }, context);// 10、准备应用上下文prepareContext(context, environment, listeners, applicationArguments,printedBanner);// 11、刷新应用上下文refreshContext(context);// 12、应用上下文刷新后置处理afterRefresh(context, applicationArguments);// 13、停止计时监控类stopWatch.stop();// 14、输出日志记录执行主类名、时间信息if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);}// 15、发布应用上下文启动完成事件listeners.started(context);// 16、执行所有 Runner 运行器callRunners(context, applicationArguments);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, listeners);throw new IllegalStateException(ex);}try {// 17、发布应用上下文就绪事件listeners.running(context);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, null);throw new IllegalStateException(ex);}// 18、返回应用上下文return context;
}

123 看解释，不做多余解释

4.获取监听器

getRunListeners同SpringApplication构造方法获取获取ApplicationListener方法一样（见上一篇）META-INF/spring.factories 中SpringApplicationRunListener实现类EventPublishingRunListener

	private SpringApplicationRunListeners getRunListeners(String[] args) {Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));}

org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener

EventPublishingRunListener初始化

	public EventPublishingRunListener(SpringApplication application, String[] args) {this.application = application;this.args = args;this.initialMulticaster = new SimpleApplicationEventMulticaster();for (ApplicationListener<?> listener : application.getListeners()) {this.initialMulticaster.addApplicationListener(listener);}}

将监听器（ApplicationListener）加入到SimpleApplicationEventMulticaster中 this.defaultRetriever.applicationListeners

[org.springframework.boot.devtools.restart.RestartApplicationListener@2584b82d, org.springframework.boot.context.config.ConfigFileApplicationListener@7bbc8656, org.springframework.boot.context.config.AnsiOutputApplicationListener@6933b6c6, org.springframework.boot.context.logging.LoggingApplicationListener@7d3e8655, org.springframework.boot.context.logging.ClasspathLoggingApplicationListener@7dfb0c0f, org.springframework.boot.autoconfigure.BackgroundPreinitializer@626abbd0, org.springframework.boot.context.config.DelegatingApplicationListener@169bb4dd, org.springframework.boot.builder.ParentContextCloserApplicationListener@1f9e9475, org.springframework.boot.ClearCachesApplicationListener@3aa078fd, org.springframework.boot.context.FileEncodingApplicationListener@d23e042, org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener@46d59067, org.springframework.boot.devtools.logger.DevToolsLogFactory$Listener@2d0399f4]

public void addApplicationListener(ApplicationListener<?> listener) {synchronized (this.retrievalMutex) {// Explicitly remove target for a proxy, if registered already,// in order to avoid double invocations of the same listener.Object singletonTarget = AopProxyUtils.getSingletonTarget(listener);if (singletonTarget instanceof ApplicationListener) {this.defaultRetriever.applicationListeners.remove(singletonTarget);}this.defaultRetriever.applicationListeners.add(listener);this.retrieverCache.clear();}}

4.1 启动监听器

跟进EventPublishingRunListener starting

	public void starting() {this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));}

线程池为空同步执行

	ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {Executor executor = getTaskExecutor();if (executor != null) {executor.execute(() -> invokeListener(listener, event));}else {invokeListener(listener, event);}}

从缓存中获取监听器如果没有通过retrieveApplicationListeners方法获取

protected Collection<ApplicationListener<?>> getApplicationListeners(ApplicationEvent event, ResolvableType eventType) {Object source = event.getSource();Class<?> sourceType = (source != null ? source.getClass() : null);ListenerCacheKey cacheKey = new ListenerCacheKey(eventType, sourceType);// Quick check for existing entry on ConcurrentHashMap...ListenerRetriever retriever = this.retrieverCache.get(cacheKey);if (retriever != null) {return retriever.getApplicationListeners();}if (this.beanClassLoader == null ||(ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {// Fully synchronized building and caching of a ListenerRetrieversynchronized (this.retrievalMutex) {retriever = this.retrieverCache.get(cacheKey);if (retriever != null) {return retriever.getApplicationListeners();}retriever = new ListenerRetriever(true);Collection<ApplicationListener<?>> listeners =retrieveApplicationListeners(eventType, sourceType, retriever);this.retrieverCache.put(cacheKey, retriever);return listeners;}}else {// No ListenerRetriever caching -> no synchronization necessaryreturn retrieveApplicationListeners(eventType, sourceType, null);}}

this.defaultRetriever.applicationListeners从这里获取监听器赋值是在SimpleApplicationEventMulticaster初始化的时候，总共是12个监听器，经过过滤剩下五个监听器

	private Collection<ApplicationListener<?>> retrieveApplicationListeners(ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable ListenerRetriever retriever) {List<ApplicationListener<?>> allListeners = new ArrayList<>();Set<ApplicationListener<?>> listeners;Set<String> listenerBeans;synchronized (this.retrievalMutex) {listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);}for (ApplicationListener<?> listener : listeners) {if (supportsEvent(listener, eventType, sourceType)) {if (retriever != null) {retriever.applicationListeners.add(listener);}allListeners.add(listener);}}if (!listenerBeans.isEmpty()) {BeanFactory beanFactory = getBeanFactory();for (String listenerBeanName : listenerBeans) {try {Class<?> listenerType = beanFactory.getType(listenerBeanName);if (listenerType == null || supportsEvent(listenerType, eventType)) {ApplicationListener<?> listener =beanFactory.getBean(listenerBeanName, ApplicationListener.class);if (!allListeners.contains(listener) && supportsEvent(listener, eventType, sourceType)) {if (retriever != null) {if (beanFactory.isSingleton(listenerBeanName)) {retriever.applicationListeners.add(listener);}else {retriever.applicationListenerBeans.add(listenerBeanName);}}allListeners.add(listener);}}}catch (NoSuchBeanDefinitionException ex) {// Singleton listener instance (without backing bean definition) disappeared -// probably in the middle of the destruction phase}}}AnnotationAwareOrderComparator.sort(allListeners);if (retriever != null && retriever.applicationListenerBeans.isEmpty()) {retriever.applicationListeners.clear();retriever.applicationListeners.addAll(allListeners);}return allListeners;}

继续主流程，每个监听器循环调用invokeListener 继续跟进会发现其实是调用每个监听器onApplicationEvent方法，触发事件org.springframework.boot.context.event.ApplicationStartingEvent

private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {try {listener.onApplicationEvent(event);}catch (ClassCastException ex) {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.isDebugEnabled()) {logger.debug("Non-matching event type for listener: " + listener, ex);}}else {throw ex;}}}

spring boot 有很多事件，大同小异触发阶段不一样，过程是一样的不在赘述