SSM-----BeanFactoryPostProcessor分析

BeanFactoryPostProcessor

是一个beanFactory的后置处理器。

执行时机

Modify the application context’s internal bean factory after its standard * initialization. All bean definitions will have been loaded, but no beans * will have been instantiated yet. This allows for overriding or adding * properties even to eager-initializing beans.

在beanFactory初始化之后，所有的bean定义已经被加载，但是bean还没有被实例化的时候执行。

执行步骤

1. 调用redresh()，刷新容器

public AnnotationConfigApplicationContext(Class<?>... componentClasses) {
   this();
   register(componentClasses);
   refresh();
}

2. 调用invokeBeanFactoryPostProcessors(beanFactory)，调用在上下文中注册为bean的工厂处理器。

// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

/**
 * 实例化并调用所有注册的BeanFactoryPostProcessor Bean，*遵循显式顺序（如果给定）。
 * 必须在单例实例化之前调用。
 */
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()));
   }
}

3. 调用PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors())

public static void invokeBeanFactoryPostProcessors(
      ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

   // 如果有的话，首先调用BeanDefinitionRegistryPostProcessors。
   Set<String> processedBeans = new HashSet<>();

   if (beanFactory instanceof BeanDefinitionRegistry) {
      BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
      List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
      List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

      for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
         if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
            BeanDefinitionRegistryPostProcessor registryProcessor =
                  (BeanDefinitionRegistryPostProcessor) postProcessor;
            // 调用BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry()方法
            registryProcessor.postProcessBeanDefinitionRegistry(registry);
            registryProcessors.add(registryProcessor);
         }
         else {
            regularPostProcessors.add(postProcessor);
         }
      }

      List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

      // 首先，调用实现了PriorityOrdered接口的BeanDefinitionRegistryPostProcessor
      String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
      for (String ppName : postProcessorNames) {
         if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
            processedBeans.add(ppName);
         }
      }
      sortPostProcessors(currentRegistryProcessors, beanFactory);
      registryProcessors.addAll(currentRegistryProcessors);
      invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
      currentRegistryProcessors.clear();

      // 然后，调用实现了Ordered接口的BeanDefinitionRegistryPostProcessor
      postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
      for (String ppName : postProcessorNames) {
         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();

      // 最后，调用没用实现接口的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();
      }

      // 现在，调用到目前为止已处理的所有处理器的BeanDefinitionRegistryPostProcessors回调。
      invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
      invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
   }

   else {
      // 调用在上下文实例中注册的工厂处理器。如果beanFactoryPostProcessor没有实现了BeanDefinitionRegistryPostProcessors接口的话，这里的beanFactoryPostProcessors.size()就是0
      invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
   }

   // 以下是对beanFactoryPostProcessor的操作
   String[] postProcessorNames =
         beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

   // 这里声明一些变量，并通过beanFactory获取实现对应接口的beanFactoryPostProcessor的名称，并存放到指定List中
   List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
   List<String> orderedPostProcessorNames = new ArrayList<>();
   List<String> nonOrderedPostProcessorNames = new ArrayList<>();
   for (String ppName : postProcessorNames) {
      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);
      }
   }

   // 首先，调用实现了PriorityOrdered接口的BeanFactoryPostProcessor
   sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
   invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

   // 然后，调用实现了Ordered接口的BeanFactoryPostProcessor
   List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
   for (String postProcessorName : orderedPostProcessorNames) {
      orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
   }
   sortPostProcessors(orderedPostProcessors, beanFactory);
   invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

   // 最后，调用没有实现接口的BeanFactoryPostProcessor
	List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
   invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
    
   // 清除bean定义缓存，因为元数据可能已经更改
   beanFactory.clearMetadataCache();
}

4. 因为我们的MyBeanPostProcessor没有实现PriorityOrdered、Ordered接口，所以是最后调用的。

invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

/**
	调用给定的BeanFactoryPostProcessor bean。
*/
private static void invokeBeanFactoryPostProcessors(
      Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {

   // 调用所有的BeanFactoryPostProcessor中的postProcessBeanFactory(beanFactory)方法
   for (BeanFactoryPostProcessor postProcessor : postProcessors) {
      postProcessor.postProcessBeanFactory(beanFactory);
   }
}

5. 执行我们的MyBeanPostProcessor中自定义的postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)方法

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    // bean定义个数
    int beanDefinitionCount = beanFactory.getBeanDefinitionCount();
    // bean定义列表
    String[] beanDefinitionNames = beanFactory.getBeanDefinitionNames();
    System.out.println("beanFactory中一共有"+beanDefinitionCount+"个bean定义");
    System.out.println(ArrayUtil.arrayToString(beanDefinitionNames));
}

本文章是博主学习SSM中的一些笔记，如有错误，请大佬指出，感谢大佬！