Spring 容器初始化之Bean的后置处理器

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本文主要涉及：Spring中Bean的后置处理加入容器过程。

6.registerBeanPostProcessors

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
 PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this); } 复制代码

  在Spring中对于 BeanPostProcessor 的处理分为两个过程，对于内置的 BeanPostProcessor的子类的实现，添加到 IoC容器中，是经过refresh() 方法中的 prepareBeanFactory() 过程来完成的。好比 ApplicationContextAwareProcessor， ApplicationListenerDetector。对于 ImportAwareBeanPostProcessor 是在，处理 ConfigurationClassPostProcessor时，对 @Configuration注解的类生成CGLIB 代理的时候加入容器中的。最后，在Spring中对于 BeanPostProcessor的实现类的处理，是在 refresh() 方法中有一个步骤 registerBeanPostProcessors() 来完成注册的，如 BeanPostProcessorChecker，CommonAnnotationBeanPostProcessor 以及 AutowiredAnnotationBeanPostProcessor，CommonAnnotationBeanPostProcessor。这样，在容器初始化之处，没有本身实现 BeanPsotProcessor 的时候，容器中就包含了6个Bean的后置处理器的实现。其中对于 registerBeanPostProcessors() 方法的详细代码实现，下面一一分析：

public static void registerBeanPostProcessors(  ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {   // 获取BeanDefinitionMap中全部的BeanPostProcessor  String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);   /**  * BeanPostProcessorChecker 是一个普通的信息打印，可能会有些状况  * 当spring 的配置中的后置处理器尚未被注册就已经开始了bean的初始化时  * 便会打印出 BeanPostProcessorChecker 中设定的值  */  int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;  // new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)  // 建立一个 默认的 PostProcessorRegistrationDelegate, BeanPostProcessorChecker 是 PostProcessorRegistrationDelegate  // 中的一个静态的内部类 且实现了 BeanPostProcessor 接口  beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));   /**  * 使用priorityOrdered 保证顺序  */  List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();  List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();  /**  * 使用 ordered 保证顺序  */  List<String> orderedPostProcessorNames = new ArrayList<>();  /**  * 无序 BeanPostProcessor  */  List<String> nonOrderedPostProcessorNames = new ArrayList<>();  for (String ppName : postProcessorNames) {  if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {  BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);  priorityOrderedPostProcessors.add(pp);  if (pp instanceof MergedBeanDefinitionPostProcessor) {  internalPostProcessors.add(pp);  }  }  else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {  orderedPostProcessorNames.add(ppName);  }  else {  nonOrderedPostProcessorNames.add(ppName);  }  }   /**  * 第一步，注册全部实现 PriorityOrdered 的 BeanPostProcessors  */  sortPostProcessors(priorityOrderedPostProcessors, beanFactory);  registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);   /**  * 第二步，注册全部实现 Ordered 的 BeanPostProcessors  */  List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();  for (String ppName : orderedPostProcessorNames) {  BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);  orderedPostProcessors.add(pp);  if (pp instanceof MergedBeanDefinitionPostProcessor) {  internalPostProcessors.add(pp);  }  }  sortPostProcessors(orderedPostProcessors, beanFactory);  registerBeanPostProcessors(beanFactory, orderedPostProcessors);   /**  * 第三步，注册无序 的 BeanPostProcessors  */  List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();  for (String ppName : nonOrderedPostProcessorNames) {  BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);  nonOrderedPostProcessors.add(pp);  if (pp instanceof MergedBeanDefinitionPostProcessor) {  internalPostProcessors.add(pp);  }  }  registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);   // Finally, re-register all internal BeanPostProcessors.  /**  * 注册全部 MergedBeanDefinitionPostProcessor 类型的 BeanPostProcessors  */  sortPostProcessors(internalPostProcessors, beanFactory);  registerBeanPostProcessors(beanFactory, internalPostProcessors);   // Re-register post-processor for detecting inner beans as ApplicationListeners,  // moving it to the end of the processor chain (for picking up proxies etc).  beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext)); } 复制代码

将Bean的后置处理器加入到容器中

public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
 Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");  // Remove from old position, if any  this.beanPostProcessors.remove(beanPostProcessor);  // Track whether it is instantiation/destruction aware  if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {  this.hasInstantiationAwareBeanPostProcessors = true;  }  if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {  this.hasDestructionAwareBeanPostProcessors = true;  }  // Add to end of list  this.beanPostProcessors.add(beanPostProcessor); } 复制代码

  至此，Spring 中容器初始化不部分的解析已经处理完了，到目前为止，容器的中的东西基本上已经齐活了，经过下面的容器造成图示例：

7.initMessageSource()

protected void initMessageSource() {
 ConfigurableListableBeanFactory beanFactory = getBeanFactory();  if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {  this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);  // Make MessageSource aware of parent MessageSource.  if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {  HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;  if (hms.getParentMessageSource() == null) {  // Only set parent context as parent MessageSource if no parent MessageSource  // registered already.  hms.setParentMessageSource(getInternalParentMessageSource());  }  }  if (logger.isTraceEnabled()) {  logger.trace("Using MessageSource [" + this.messageSource + "]");  }  }  else {  // Use empty MessageSource to be able to accept getMessage calls.  DelegatingMessageSource dms = new DelegatingMessageSource();  dms.setParentMessageSource(getInternalParentMessageSource());  this.messageSource = dms;  beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);  if (logger.isTraceEnabled()) {  logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");  }  } } 复制代码

  判断beanFactory中是否有名字为messageSource的bean，若是有，从beanFactory中获取而且判断获取的是否是HierarchicalMessageSource类型的，若是是设置其父级消息源 若是没有，新建DelegatingMessageSource类做为messageSource的Bean。

8.initApplicationEventMulticaster()

protected void initApplicationEventMulticaster() {
 ConfigurableListableBeanFactory beanFactory = getBeanFactory();  if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {  this.applicationEventMulticaster =  beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);  if (logger.isTraceEnabled()) {  logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");  }  }  else {  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() + "]");  }  } } 复制代码

  初始化 ApplicationEventMulticaster 若是用户自定义了事件广播器，那么使用用户自定义的事件广播器若是用户没有自定义事件广播器，那么使用默认的 ApplicationEventMulticaster 即 SimpleApplicationEventMulticaster.

9.onRefresh()

protected void onRefresh() throws BeansException {
 // For subclasses: do nothing by default. } 复制代码

  空方法，Spring 预留给子类须要时来实现。

10.registerListeners();

protected void registerListeners() {
 // Register statically specified listeners first.  // 硬编码的方式注册监听器的处理  for (ApplicationListener<?> listener : getApplicationListeners()) {  getApplicationEventMulticaster().addApplicationListener(listener);  }   // Do not initialize FactoryBeans here: We need to leave all regular beans  // uninitialized to let post-processors apply to them!  // 配置文件注册监听器的处理  String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);  for (String listenerBeanName : listenerBeanNames) {  getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);  }   // Publish early application events now that we finally have a multicaster...  Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;  this.earlyApplicationEvents = null;  if (earlyEventsToProcess != null) {  for (ApplicationEvent earlyEvent : earlyEventsToProcess) {  getApplicationEventMulticaster().multicastEvent(earlyEvent);  }  } } 复制代码

  获取容器中的监听器，而后获得当前容器中的 applicationEventMulticaster，调用 addApplicationListener进行添加。 这里的 applicationEventMulticaster 就是刚才初始化的，若是为空就是 SimpleApplicationEventMulticaster。

  从BeanFactory中获取ApplicationListener类型的Bean，而且添加为ListenerBeans。

  获取须要提早发布的事件，进行广播。

最后

  至此， refresh()方法中的各个子方法的学习，仅剩了一个finishBeanFactoryInitialization()。关于这个方法，涉及到不少新的过程 而且与 Bean 的实例化过程息息相关。后面的文章将会介绍 Bean 的实例化。这里就是Bean的实例化入口的地方。

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