Spring源码之九finishRefresh详解

Spring源码之九finishRefresh详解

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Spring IoC 的核心内容要收尾了，本文将对最后一个方法 finishRefresh 进行介绍，位于refresh 方法中的第九个位置。

本章实际是对发布订阅模式的一种补充，这是Spring在刷新事件完成后发布事件。

由于存在上下文关系，本文也会对 initApplicationEventMulticaster 方法、registerListeners 方法进行回顾。

我们回到refresh 方法中。

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			//1、刷新前的准备
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			//2、将会初始化 BeanFactory、加载 Bean、注册 Bean
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			//3、设置 BeanFactory 的类加载器，添加几个 BeanPostProcessor，手动注册几个特殊的 bean
			prepareBeanFactory(beanFactory);

			try {
				//4、模板方法
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				//执行BeanFactory后置处理器
				invokeBeanFactoryPostProcessors(beanFactory);

				// 5、Register bean processors that intercept bean creation.
				//注册bean后置处理器
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				//国际化
				initMessageSource();

				// Initialize event multicaster for this context.
				//初始化事件广播器
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				//6、模板方法--springboot实现了这个方法
				onRefresh();

				// Check for listener beans and register them.
				//7、注册监听器
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				//8、完成bean工厂的初始化**方法重要**********************************************
				finishBeanFactoryInitialization(beanFactory);

				//9、 Last step: publish corresponding event.
				//完成上下文的刷新工作
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

我们首先知道这个三个方法的作用：

initApplicationEventMulticaster()：初始化应用的事件广播器

/**
	 * Initialize the ApplicationEventMulticaster.
	 * Uses SimpleApplicationEventMulticaster if none defined in the context.
	 * @see org.springframework.context.event.SimpleApplicationEventMulticaster
	 */
	protected void initApplicationEventMulticaster() {
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		// 1.判断BeanFactory是否已经存在事件广播器（固定使用beanName=applicationEventMulticaster）
		if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
			// 1.1 如果已经存在，则将该bean赋值给applicationEventMulticaster
			this.applicationEventMulticaster =
					beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
			if (logger.isTraceEnabled()) {
				logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
			}
		}
		else {
			// 1.2 如果不存在，则使用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() + "]");
			}
		}
	}

最终只做了一件事，初始化应用的事件广播器。（具体什么是事件广播器及其作用可见上上篇文章，具体就不在吃赘述了）

registerListeners()：注册监听器。见上上篇文章

finishRefresh()：完成上下文的刷新工作，本文重点。

首先概览finishRefresh方法

	protected void finishRefresh() {
		// Clear context-level resource caches (such as ASM metadata from scanning).
		//清除资源缓存
		clearResourceCaches();

		// Initialize lifecycle processor for this context.
		// // 1.为此上下文初始化生命周期处理器
		initLifecycleProcessor();

		// Propagate refresh to lifecycle processor first.
		// 2.首先将刷新完毕事件传播到生命周期处理器（触发isAutoStartup方法返回true的SmartLifecycle的start方法）
		getLifecycleProcessor().onRefresh();

		// Publish the final event.
		// 3.推送上下文刷新完毕事件到相应的监听器
		publishEvent(new ContextRefreshedEvent(this));

		// Participate in LiveBeansView MBean, if active.
		LiveBeansView.registerApplicationContext(this);
	}

1、2、3是重点内容

1.为此上下文初始化生命周期处理器

	protected void initLifecycleProcessor() {
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		// 1.判断BeanFactory是否已经存在生命周期处理器（固定使用beanName=lifecycleProcessor）
		if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
			this.lifecycleProcessor =
					beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
			if (logger.isTraceEnabled()) {
				logger.trace("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
			}
		}
		else {
			// 1.2 如果不存在，则使用DefaultLifecycleProcessor
			DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
			defaultProcessor.setBeanFactory(beanFactory);
			this.lifecycleProcessor = defaultProcessor;
			// 并将DefaultLifecycleProcessor作为默认的生命周期处理器，注册到BeanFactory中
			beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
			if (logger.isTraceEnabled()) {
				logger.trace("No '" + LIFECYCLE_PROCESSOR_BEAN_NAME + "' bean, using " +
						"[" + this.lifecycleProcessor.getClass().getSimpleName() + "]");
			}
		}
	}

2.首先将刷新完毕事件传播到生命周期处理器

private void startBeans(boolean autoStartupOnly) {
		// 1.获取所有的Lifecycle bean
		Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();

		// 将Lifecycle bean 按阶段分组，阶段通过实现Phased接口得到
		Map<Integer, LifecycleGroup> phases = new HashMap<>();
		// 2.遍历所有Lifecycle bean，按阶段值分组
		lifecycleBeans.forEach((beanName, bean) -> {
			// autoStartupOnly=true代表是ApplicationContext刷新时容器自动启动；autoStartupOnly=false代表是通过显示的调用启动
			// 3.当autoStartupOnly=false，也就是通过显示的调用启动，会触发全部的Lifecycle；
			// 当autoStartupOnly=true，也就是ApplicationContext刷新时容器自动启动，只会触发isAutoStartup方法返回true的SmartLifecycle

			if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
				// 3.1 获取bean的阶段值（如果没有实现Phased接口，则值为0）
				int phase = getPhase(bean);
				// 3.2 拿到存放该阶段值的LifecycleGroup
			   LifecycleGroup group = phases.get(phase);
				if (group == null) {
					// 3.3 如果该阶段值的LifecycleGroup为null，则新建一个
					group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
					phases.put(phase, group);
				}
				// 3.4 将bean添加到该LifecycleGroup
				group.add(beanName, bean);
			}
		});
		// 4.如果phases不为空
		if (!phases.isEmpty()) {
			List<Integer> keys = new ArrayList<>(phases.keySet());
			// 4.1 按阶段值进行排序
			Collections.sort(keys);
			// 4.2 按阶段值顺序，调用LifecycleGroup中的所有Lifecycle的start方法
			for (Integer key : keys) {
				phases.get(key).start();
			}
		}
	}

3.推送上下文刷新完毕事件到相应的监听器

protected void publishEvent(Object event, @Nullable ResolvableType eventType) {
		Assert.notNull(event, "Event must not be null");

		// Decorate event as an ApplicationEvent if necessary
		// 1.如有必要，将事件装饰为ApplicationEvent
		ApplicationEvent applicationEvent;
		if (event instanceof ApplicationEvent) {
			applicationEvent = (ApplicationEvent) event;
		}
		else {
			applicationEvent = new PayloadApplicationEvent<>(this, event);
			if (eventType == null) {
				eventType = ((PayloadApplicationEvent<?>) applicationEvent).getResolvableType();
			}
		}

		// Multicast right now if possible - or lazily once the multicaster is initialized
		if (this.earlyApplicationEvents != null) {
			this.earlyApplicationEvents.add(applicationEvent);
		}
		else {
			// 2.使用事件广播器广播事件到相应的监听器
			getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
		}

		// Publish event via parent context as well...
		// 3.同样的，通过parent发布事件.....
		if (this.parent != null) {
			if (this.parent instanceof AbstractApplicationContext) {
				((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
			}
			else {
				this.parent.publishEvent(event);
			}
		}
	}

这里面调用的publishEvent方法，和我们自定义的监听器调用的publishEvent是同一个方法，ContextRefreshedEvent是Spirng的一个事件称为上下文刷新完毕事件，如果我们在上下文刷新完成后要写一个发布事件，实现ApplicationListener接口即可。

我们在此举一个简单的例子。

这样，当 Spring 执行到 finishRefresh 方法时，就会将 ContextRefreshedEvent 事件推送到 MyRefreshedListener 中。

读者可以结合自定义事件对比一个和Spring提供的刷新上下文事件的区别，以便于更好的理解Spring的事件监听机制。

跟 ContextRefreshedEvent 相似的还有：ContextStartedEvent、ContextClosedEvent、ContextStoppedEvent。

好啦，Spirng的refresh方法到这里就结束啦，一共是九篇博客，实际上这也是Spirng的IOC的全部内容了，如果读者能把九篇的完全消化，那么spring的IOC也就理解的七七八八了。