Spring Boot2 源码 run getRunListeners方法 （二）

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：true
    configureHeadlessProperty();
 
    // 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 ListenerRetriever
			synchronized (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 necessary
			return 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

5.初始化默认应用参数类

想了解的可以看下SimpleCommandLineArgsParser类