invokeBeanFactoryPostProcessors的理解-创新互联

Spring中有两个非常重要的扩展点：

• BeanFactoryPostProcessor
• BeanPostProcessor
  其中第一个是可以对BeanDefinition注册时进行扩展，而第二个是对spring中IOC容器中的对象进行实例化的时候进行扩展。
  今天主要谈一下对BeanFactoryPostProcessor的几点理解：

• 这是个重要的接口，其还有一个子接口：BeanDefinitionRegistryPostProcessor：
  
• 在spring容器的启动过程，对所有组件的注册主要就是通过对这两个接口的处理来完成的。
• spring启动时，最主要的方法就是refresh方法：

public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {	// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {		// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

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

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

			catch (BeansException ex) {		if (logger.isWarnEnabled()) {logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}

			finally {		// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

• 其中，invokeBeanFactoryPostProcessors这个方法，就是处理容器中所有bean的注册过程
• invokeBeanFactoryPostProcessors这个方法具体如下：

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()));
		}
	}

• 这个方法，其实只有第一条语句中的invokeBeanFactoryPostProcessors方法，是重要且对容器bean注册有效
• 这个方法传入的参数第一个是工厂，第二个参数是BeanFactoryPostProcessor的list
• 正常启动的时候，如果我们不做处理，那么第二个参数就是一个空的list
• 我们也可以在代码中进行BeanFactoryPostProcessor的注入
• spring容器启动到这里时，会自动注册5个bean：
  

上述图片中：

1. 第一个ConfigurationClassPostProcessor，实现的是BeanDefinitionRegistryPostProcessor接口，是最主要的扫描和注册
2. 第三个EventListenerMethodProcessor，实现BeanFactoryPostProcessor接口，与事件相关的处理组件
3. 第四个和第五个实现BeanPostProcessor接口，参与对象创建过程中的注入等处理

• 在invokeBeanFactoryPostProcessors方法中，spring会通过所有BeanFactoryPostProcessor的功能，来扫描并注册所有的bean，从方法名称来看，其作用就是调用所有的BeanFactoryPostProcessor，

其主要处理流程如下：

1. 对传入的BeanFactoryPostProcessor进行处理，添加进等待运行的列表中
   
2. 对实现了BeanDefinitionRegistryPostProcessor以及PriorityOrdered接口的组件进行实例化，并调用BeanDefinitionRegistryPostProcessor接口方法，此时，就是调用ConfigurationClassPostProcessor这个组件，来进行容器中bean的注册，具体的注册过程此处略过不表

// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
			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();

3. 对实现了BeanDefinitionRegistryPostProcessor以及Ordered接口的组件进行实例化，并调用相应接口方法

// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
			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();

4. 对只实现了BeanDefinitionRegistryPostProcessor接口的组件进行实例化，并调用相应接口方法

// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
			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();
			}

6. 对实现了BeanDefinitionRegistryPostProcessor的组件，调用其父接口BeanFactoryPostProcessor的方法

// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);

7. 对实现了BeanFactoryPostProcessor以及PriorityOrdered接口的组件，调用相应接口中的方法

// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

8. 对实现了BeanFactoryPostProcessor以及Ordered接口的组件进行实例化，并调用相应接口方法

// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
		ListorderedPostProcessors = new ArrayList<>();
		for (String postProcessorName : orderedPostProcessorNames) {	orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		sortPostProcessors(orderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

9. 对只实现了BeanFactoryPostProcessor接口的组件进行实例化，并调用相应接口方法

// Finally, invoke all other BeanFactoryPostProcessors.
		ListnonOrderedPostProcessors = new ArrayList<>();
		for (String postProcessorName : nonOrderedPostProcessorNames) {	nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

总结：

• 此方法主要作用，就是按照顺序分别调用实现了BeanDefinitionRegistryPostProcessor接口的组件以及实现了BeanFactoryPostProcessor接口的组件；其中最主要的组件就是ConfigurationClassPostProcessor，其实现的是子接口，实现的方法功能，就是对容器中进行beanDefinition的注册。

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