spring源码分析-BeanFactoryPostProcessor

• spring-系列
• 前言
• BeanFactoryPostProcessor介绍
• • BeanFactoryPostProcessor
  • BeanDefinitionRegistryPostProcessor
  • 小结
• BeanFactoryPostProcessor原理
• • invokeBeanFactoryPostProcessors
• 总结

BeanFactoryPostProcessor是BeanFactory的一个钩子接口，更是一种扩展，也正是因为这个接口造就了spring加载Bean的方式变得多种多样。我相信大部分开发人员对这个接口可能还存在一些陌生，毕竟这个接口是属于一种底层扩展，如果你是一个spring插件开发者，那一定对这个接口很熟悉。本文从源码的角度来分析spring是如何通过BeanDefinitionRegistryPostProcessor来加载Bean。

我们从源码查看BeanFactoryPostProcessor的层次结构，发现它还有一个子接口BeanDefinitionRegistryPostProcessor，代码结构如下：

@FunctionalInterface
public interface BeanFactoryPostProcessor {

	
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

根据源码我们知道只有一个方法postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)，我们是通过这个BeanFactory来增强BeanFactory的功能。

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

	
	void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

}

根据源码我们知道只有一个方法postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)，这个方法很明显是为了Bean的注册而生了，BeanDefinitionRegistry 是BeanDefinition的注册器，而注册Bean的过程是将满足Bean条件的类解析为BeanDefinition对象然后注册到BeanDefinition注册器中。

BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor都是扩展Bean的加载方式，当我们需要自定义自己的Bean加载方式时实现BeanDefinitionRegistryPostProcessor接口即可。@Configuration注解的实现就是基于BeanDefinitionRegistryPostProcessor接口完成。

看过spring源码的读者都很清楚AbstractApplicationContext类中refresh()是spring加载Bean的核心方法，大部分的处理逻辑都是在这个方法中完成，代码如下：

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

			// 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);

				
				StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
				// Invoke factory processors registered as beans in the context.
				
				invokeBeanFactoryPostProcessors(beanFactory);

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

				// 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();
				contextRefresh.end();
			}
		}
	}

根据源码发现spring在invokeBeanFactoryPostProcessors(beanFactory)方法中是实现BeanFactoryPostProcessors的具体逻辑，下面根据这个方法来分析处理逻辑。

	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 (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}
	}

逻辑处理核心是PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors())方法，下面分析：

public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {
		Set processedBeans = new HashSet<>();

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


			


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

			
			List currentRegistryProcessors = new ArrayList<>();

			// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
			// 首先，调用实现PriorityOrdered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, beanFactory.getApplicationStartup());
			currentRegistryProcessors.clear();

			// 接下来，调用实现Ordered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, beanFactory.getApplicationStartup());
			currentRegistryProcessors.clear();

			// 最后，调用所有其他BeanDefinitionRegistryPostProcessor，直到不再出现其他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, beanFactory.getApplicationStartup());
				currentRegistryProcessors.clear();
			}

			
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		}

		else {
			// Invoke factory processors registered with the context instance.
			invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
		}

		

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let the bean factory post-processors apply to them!
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

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

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

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

		// Finally, invoke all other BeanFactoryPostProcessors.
		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();
	}


	
	private static void sortPostProcessors(List postProcessors, ConfigurableListableBeanFactory beanFactory) {
		// Nothing to sort?
		if (postProcessors.size() <= 1) {
			return;
		}
		Comparator