摘要: 本文结合《Spring源码深度解析》来分析Spring 5.0.6版本的源代码。若有描述错误之处,欢迎指正。
在 Spring 中还提供了 Lifecycle 接口, Lifecycle 中包含start/stop方法,实现此接口后Spring会保证在启动的时候调用其start方法开始生命周期,并在Spring关闭的时候调用 stop方法来结束生命周期,通常用来配置后台程序,在启动后一直运行(如对 MQ 进行轮询等)。而ApplicationContext的初始化最后正是保证了这一功能的实现。
/** * Finish the refresh of this context, invoking the LifecycleProcessor's * onRefresh() method and publishing the * {@link org.springframework.context.event.ContextRefreshedEvent}. */ protected void finishRefresh() { // Clear context-level resource caches (such as ASM metadata from scanning). clearResourceCaches(); // Initialize lifecycle processor for this context. initLifecycleProcessor(); // Propagate refresh to lifecycle processor first. getLifecycleProcessor().onRefresh(); // Publish the final event. publishEvent(new ContextRefreshedEvent(this)); // Participate in LiveBeansView MBean, if active. LiveBeansView.registerApplicationContext(this); }
一、initLifecycleProcessor
当ApplicationContext启动或停止时,它会通过LifecycleProcessor来与所有声明的bean的周期做状态更新,而在LifecycleProcessor的使用前首先需要初始化。
/** * Initialize the LifecycleProcessor. * Uses DefaultLifecycleProcessor if none defined in the context. * @see org.springframework.context.support.DefaultLifecycleProcessor */ protected void initLifecycleProcessor() { ConfigurableListableBeanFactory beanFactory = getBeanFactory(); 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 { DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor(); defaultProcessor.setBeanFactory(beanFactory); this.lifecycleProcessor = defaultProcessor; beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor); if (logger.isTraceEnabled()) { logger.trace("Unable to locate LifecycleProcessor with name '" + LIFECYCLE_PROCESSOR_BEAN_NAME + "': using default [" + this.lifecycleProcessor + "]"); } } }
二、onRefresh
启动所有实现了Lifecycle接口的bean。
@Override public void onRefresh() { startBeans(true); this.running = true; } // Internal helpers private void startBeans(boolean autoStartupOnly) { Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans(); Map<Integer, LifecycleGroup> phases = new HashMap<>(); lifecycleBeans.forEach((beanName, bean) -> { if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) { int phase = getPhase(bean); LifecycleGroup group = phases.get(phase); if (group == null) { group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly); phases.put(phase, group); } group.add(beanName, bean); } }); if (!phases.isEmpty()) { List<Integer> keys = new ArrayList<>(phases.keySet()); Collections.sort(keys); for (Integer key : keys) { phases.get(key).start(); } } }
三、publishEvent
当完成ApplicationContext初始化的时候,要通过Spring中的事件发布机制来发出ContextRefreshedEvent事件,以保证对应的监听器可以做进一步的逻辑处理。
/** * Publish the given event to all listeners. * <p>Note: Listeners get initialized after the MessageSource, to be able * to access it within listener implementations. Thus, MessageSource * implementations cannot publish events. * @param event the event to publish (may be an {@link ApplicationEvent} * or a payload object to be turned into a {@link PayloadApplicationEvent}) */ @Override public void publishEvent(Object event) { publishEvent(event, null); } /** * Publish the given event to all listeners. * @param event the event to publish (may be an {@link ApplicationEvent} * or a payload object to be turned into a {@link PayloadApplicationEvent}) * @param eventType the resolved event type, if known * @since 4.2 */ protected void publishEvent(Object event, @Nullable ResolvableType eventType) { Assert.notNull(event, "Event must not be null"); // Decorate event as an ApplicationEvent if necessary 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 { getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType); } // Publish event via parent context as well... if (this.parent != null) { if (this.parent instanceof AbstractApplicationContext) { ((AbstractApplicationContext) this.parent).publishEvent(event, eventType); } else { this.parent.publishEvent(event); } } }