[Java] Spring的BeanFactoryPostProcessor接口示例代码详解

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
 
    // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
    // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
    if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
      beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
      beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }
  }

public static void invokeBeanFactoryPostProcessors(
      ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
   // 用于存放已经处理过的Bean名字
    Set<String> processedBeans = new HashSet<>();
   // 一般会进入这个判断
    if (beanFactory instanceof BeanDefinitionRegistry) {
      BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
  // 所谓的regularPostProcessors就是指实现BeanFactoryPostProcessor接口的Bean
      List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
  // 所谓的registryProcessors就是指实现BeanDefinitionRegistryPostProcessor接口的Bean
      List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
  // 这边遍历的是通过ApplicationContext接口注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor接口
  // 需要和BeanFactory中BeanDefinitionMap中的BeanFactoryPostProcessor接口区分开
      for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
        if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
          BeanDefinitionRegistryPostProcessor registryProcessor =
              (BeanDefinitionRegistryPostProcessor) postProcessor;
    //如果是BeanDefinitionRegistryPostProcessor，则先进行postProcessBeanDefinitionRegistry处理，这个方法一般进行BeanDefinition注册，从这边可以看出BeanDefinitionRegistryPostProcessor接口的方法先调用，所以优先级高于BeanFactoryPostProcessor
    // 通过这个代码可以看出，通过ApplicationContext直接注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor并不支持Order接口，而是根据注册的顺序执行
          registryProcessor.postProcessBeanDefinitionRegistry(registry);
    // 保存这个BeanDefinitionRegistryPostProcessor，因为还要执行这个类的BeanFactoryPostProcessor方法；
          registryProcessors.add(registryProcessor);
        }
        else {
    // 保存，后面还要执行这个类的BeanFactoryPostProcessor方法；
          regularPostProcessors.add(postProcessor);
        }
      }
 
      List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
  // 这边获取的是BeanFactory中的BeanDefinitionRegistryPostProcessor
      String[] postProcessorNames =
          beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
      for (String ppName : postProcessorNames) {
   //先处理PriorityOrdered标注的BeanDefinitionRegistryPostProcessor
        if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
          currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
    //将其标记为已经处理,防止重复处理
          processedBeans.add(ppName);
        }
      }
  // 将其排序，以便按顺序处理
      sortPostProcessors(currentRegistryProcessors, beanFactory);
  // 将其保存，以便处理这个类的BeanFactoryPostProcessor方法
      registryProcessors.addAll(currentRegistryProcessors);
  // 执行BeanDefinitionRegistryPostProcessor接口方法
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
  // 清除，以便开始处理@Order标注的注解
      currentRegistryProcessors.clear();
  
  // 注意：这边重新获取BeanDefinitionRegistryPostProcessor是有深意的，因为上面在处理@PriorityOrdered标注的BeanDefinitionRegistryPostProcessor时可能又注入了新的BeanDefinitionRegistryPostProcessor。
      postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
      for (String ppName : postProcessorNames) {
   // 判断是否处理过，防止重复处理，下面的逻辑和上面相同， 不介绍了
        if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
          currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
          processedBeans.add(ppName);
        }
      }
      sortPostProcessors(currentRegistryProcessors, beanFactory);
      registryProcessors.addAll(currentRegistryProcessors);
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
      currentRegistryProcessors.clear();
 
  // 处理不标注注解的BeanDefinitionRegistryPostProcessor
      boolean reiterate = true;
      while (reiterate) {
        reiterate = false;
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
          if (!processedBeans.contains(ppName)) {
            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
            processedBeans.add(ppName);
            reiterate = true;
          }
        }
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        registryProcessors.addAll(currentRegistryProcessors);
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        currentRegistryProcessors.clear();
      }
 
      // 调用postProcessBeanFactory 方法，所以BeanDefinitionRegistryPostProcessor中的postProcessBeanFactory方法的优先级要高。
      invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
      invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    }
 
    else {
      // Invoke factory processors registered with the context instance.
      invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }
 
    // 开始处理BeanFactoryPostProcessor接口
    String[] postProcessorNames =
        beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
 
    // 也是按照@PriorityOrdered @Ordered 和普通的方式进行处理
    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    List<String> orderedPostProcessorNames = new ArrayList<>();
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    for (String ppName : postProcessorNames) {
  // 可能已经处理过
      if (processedBeans.contains(ppName)) {
        // skip - already processed in first phase above
      }
      else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
        priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
      }
      else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
        orderedPostProcessorNames.add(ppName);
      }
      else {
        nonOrderedPostProcessorNames.add(ppName);
      }
    }
   // 先执行@PriorityOrdered标注的接口
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
   // 处理@Order标注的类
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
    for (String postProcessorName : orderedPostProcessorNames) {
  // 这边通过名字重新拿了Bean，应该是怕上面的处理改变了Bean
      orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    sortPostProcessors(orderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
 
    // 最后调用普通的BeanFactoryPostProcessor
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    for (String postProcessorName : nonOrderedPostProcessorNames) {
      nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
 
    // Clear cached merged bean definitions since the post-processors might have
    // modified the original metadata, e.g. replacing placeholders in values...
    beanFactory.clearMetadataCache();
  }

具体过程如下：假如通过ApplicationContext注册了一个BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor，那么会先执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法，但是BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法和BeanFactoryPostProcessor的postProcessBeanFactory方法暂时都不会在这步执行。
另外需要注意的是：通过ApplicationContext注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor都不支持@PriorityOrdered和@Ordered顺序处理，而是按照我们添加的顺序处理