Spring源码之九finishRefresh详解
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Spring IoC 的核心内容要收尾了，本文将对最初一个办法 finishRefresh 进行介绍，位于refresh 办法中的第九个地位。
本章理论是对公布订阅模式的一种补充，这是Spring在刷新事件实现后公布事件。
因为存在上下文关系，本文也会对 initApplicationEventMulticaster 办法、registerListeners 办法进行回顾。
咱们回到refresh 办法中。
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. //1、刷新前的筹备 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，增加几个 BeanPostProcessor，手动注册几个非凡的 bean prepareBeanFactory(beanFactory); try { //4、模板办法 // 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. //初始化事件播送器 initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. //6、模板办法--springboot实现了这个办法 onRefresh(); // Check for listener beans and register them. //7、注册监听器 registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. //8、实现bean工厂的初始化**办法重要********************************************** finishBeanFactoryInitialization(beanFactory); //9、 Last step: publish corresponding event. //实现上下文的刷新工作 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(); } } }咱们首先晓得这个三个办法的作用：
initApplicationEventMulticaster()：初始化利用的事件播送器
/** * 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是否曾经存在事件播送器（固定应用beanName=applicationEventMulticaster） if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) { // 1.1 如果曾经存在，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，则应用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，初始化利用的事件播送器。（具体什么是事件播送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()：实现上下文的刷新工作，本文重点。
首先概览finishRefresh办法
protected void finishRefresh() { // Clear context-level resource caches (such as ASM metadata from scanning). //革除资源缓存 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.首先将刷新结束事件流传到生命周期处理器（触发isAutoStartup办法返回true的SmartLifecycle的start办法） getLifecycleProcessor().onRefresh(); // Publish the final event. // 3.推送上下文刷新结束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是否曾经存在生命周期处理器（固定应用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，则应用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.首先将刷新结束事件流传到生命周期处理器
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接口失去 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刷新时容器主动启动；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，会触发全副的Lifecycle； // 当autoStartupOnly=true，也就是ApplicationContext刷新时容器主动启动，只会触发isAutoStartup办法返回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 拿到寄存该阶段值的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增加到该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 按阶段值程序，调用LifecycleGroup中的所有Lifecycle的start办法 for (Integer key : keys) { phases.get(key).start(); } } }3.推送上下文刷新结束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，将事件装璜为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.应用事件播送器播送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公布事件..... if (this.parent != null) { if (this.parent instanceof AbstractApplicationContext) { ((AbstractApplicationContext) this.parent).publishEvent(event, eventType); } else { this.parent.publishEvent(event); } } }这外面调用的publishEvent办法，和咱们自定义的监听器调用的publishEvent是同一个办法，ContextRefreshedEvent是Spirng的一个事件称为上下文刷新结束事件，如果咱们在上下文刷新实现后要写一个公布事件，实现ApplicationListener<ContextRefreshedEvent>接口即可。
咱们在此举一个简略的例子。
这样，当 Spring 执行到 finishRefresh 办法时，就会将 ContextRefreshedEvent 事件推送到 MyRefreshedListener 中。
读者能够联合自定义事件比照一个和Spring提供的刷新上下文事件的区别，以便于更好的了解Spring的事件监听机制。
跟 ContextRefreshedEvent 类似的还有：ContextStartedEvent、ContextClosedEvent、ContextStoppedEvent。
好啦，Spirng的refresh办法到这里就完结啦，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齐全消化，那么spring的IOC也就了解的七七八八了。