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 beanFactoryPostProcessors) {
   // 用于存放已经处理过的Bean名字
		Set 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 regularPostProcessors = new ArrayList<>();
    // 所谓的registryProcessors就是指实现BeanDefinitionRegistryPostProcessor接口的Bean
			List 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 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 priorityOrderedPostProcessors = new ArrayList<>();
		List orderedPostProcessorNames = new ArrayList<>();
		List 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 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 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();
	}