Spring源码(一)：深入BeanPostProcessor源码—1

1.什么是BeanPostProcessor？

         BeanPostProcessor是一个接口，作用在Bean对象实例化和依赖注入完成后、在调用初始化方法前后添加我们自己的逻辑。源码如下：

public interface BeanPostProcessor {
    /**
     *    初始化方法调用前执行
     */
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

	/**
     *   初始化方法调用后执行
     */
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

}

2.BeanPostProcessor对象如何注册到SpringIOC容器中的？

   1).BeanPostProcessor对象搜集整体来讲有三个地方：

• AnnotationConfigUtils.registerAnnotationConfigProcessors():注册了一些BeanPostProcessor

  //注入了默认的BeanFactoryPostProcessor、BeanPostProcessor
  	public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
  			BeanDefinitionRegistry registry, @Nullable Object source) {
  
  		DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
  		if (beanFactory != null) {
  			if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
  				beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
  			}
  			if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
  				beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
  			}
  		}
  
  		Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
  
  		//非常重要：5
  		if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  		//非常重要：5
  		if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  
  		if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  		//非常重要：5
  		// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
  		if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  
  		// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
  		if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition();
  			try {
  				def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
  						AnnotationConfigUtils.class.getClassLoader()));
  			}
  			catch (ClassNotFoundException ex) {
  				throw new IllegalStateException(
  						"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
  			}
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  		//非常重要：5
  		if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
  		}
  		//非常重要：5
  		if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
  		}
  
  		return beanDefs;
  	}

• invokeBeanFactoryPostProcessors()注解扫描、第三方jar包定义的BeanPostProcessor
• xml文件自定义的BeanPostProcessor。

   2).BeanPostProcessor的实例化、注册?

        BeanPostProcessor的实例化：    

public static void registerBeanPostProcessors(
			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

		// Register BeanPostProcessorChecker that logs an info message when
		// a bean is created during BeanPostProcessor instantiation, i.e. when
		// a bean is not eligible for getting processed by all BeanPostProcessors.
		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

		// Separate between BeanPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
		List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
		List<String> orderedPostProcessorNames = new ArrayList<>();
		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);
			}
		}

		// First, register the BeanPostProcessors that implement PriorityOrdered.
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

		// Next, register the BeanPostProcessors that implement Ordered.
		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);

		// Now, register all regular 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.
		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));
	}

       BeanPostProcessor的注册：     

3.源码调用的具体位置？

    1).AbstractAutowireCapableBeanFactory的doCreateBean方法中调用initializeBean方法，

    2).在invokeInitMethods方法前后分别调用了applyBeanPostProcessorsBeforeInitialization方法和applyBeanPostProcessorsAfterInitialization方法。

    3.在applyBeanPostProcessorsBeforeInitialization、applyBeanPostProcessorsAfterInitialization

方法中分别调用了BeanPostProcessor的postProcessBeforeInitialization、postProcessAfterInitialization方法。

4.BeanPostProcessor使用场景？

   1).ApplicationContextAwareProcessor执行了一堆的Aware接口的调用。代码如下：

   2).ImportAwareBeanPostProcessor执行了ImportAware接口的调用。代码如下：

   3).InitDestroyAnnotationBeanPostProcessor执行@PostConstruct注解的方法。代码如下：

       (1）findLifecycleMetadata(bean.getClass())封装@PostConstruct注解的方法.

       (2).反射调用@PostConstruct注解的方法。

   4). AbstractAutoProxyCreator给需要的对象创建代理对象。代码如下：

    5). ApplicationListenerDetector是不是监听器类型，如果是添加到广播器(监听器列表)。代码如下:

               Spring源码——深入BeanPostProcessor源码—2

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