Spring ApplicationContext（十）finishRefresh

ApplicationContext（十）finishRefresh

Spring 系列目录(https://www.cnblogs.com/binarylei/p/10198698.html)

经过以上 11 步，ApplicationContext 的刷新工作基本完成，就剩下最后一点收尾的工作。

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。

protected void finishRefresh() {
    // 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 initLifecycleProcessor 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。

protected void initLifecycleProcessor() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
        this.lifecycleProcessor =
                beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
    }
    else {
        DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
        defaultProcessor.setBeanFactory(beanFactory);
        this.lifecycleProcessor = defaultProcessor;
        beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
    }
}

二、onRefresh

启动所有实现了 Lifecycle 接口的 bean

public void onRefresh() {
    startBeans(true);
    this.running = true;
}

// Spring 内部用
private void startBeans(boolean autoStartupOnly) {
    Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
    Map<Integer, LifecycleGroup> phases = new HashMap<Integer, LifecycleGroup>();
    for (Map.Entry<String, ? extends Lifecycle> entry : lifecycleBeans.entrySet()) {
        Lifecycle bean = entry.getValue();
        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(entry.getKey(), bean);
        }
    }
    if (phases.size() > 0) {
        List<Integer> keys = new ArrayList<Integer>(phases.keySet());
        Collections.sort(keys);
        for (Integer key : keys) {
            phases.get(key).start();
        }
    }
}

3. 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。

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

    // 1. 如果 event 不是 ApplicationEvent，则需要进行封装成 PayloadApplicationEvent
    ApplicationEvent applicationEvent;
    if (event instanceof ApplicationEvent) {
        applicationEvent = (ApplicationEvent) event;
    }
    else {
        applicationEvent = new PayloadApplicationEvent<Object>(this, event);
        if (eventType == null) {
            eventType = ResolvableType.forClassWithGenerics(PayloadApplicationEvent.class, event.getClass());
        }
    }

    // 2. 发布事件 event，如果多播器懒加载，还没有初始化则将该事件先放到 earlyApplicationEvents 容器中
    //    等待多播器创建好了再发布事件 ???
    if (this.earlyApplicationEvents != null) {
        this.earlyApplicationEvents.add(applicationEvent);
    }
    else {
        getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
    }

    // 3. 父容器中也需要发布该事件 event
    if (this.parent != null) {
        if (this.parent instanceof AbstractApplicationContext) {
            ((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
        }
        else {
            this.parent.publishEvent(event);
        }
    }
}

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