Spring源码之九finishRefresh详解
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。