spring-系列

文章目录

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

前言

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。

BeanFactoryPostProcessor介绍

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：

BeanFactoryPostProcessor

@FunctionalInterface
public interface BeanFactoryPostProcessor {

	/**
	 * 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.
	 * @param beanFactory the bean factory used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	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。

BeanDefinitionRegistryPostProcessor

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

	/**
	 * Modify the application context's internal bean definition registry after its
	 * standard initialization. All regular bean definitions will have been loaded,
	 * but no beans will have been instantiated yet. This allows for adding further
	 * bean definitions before the next post-processing phase kicks in.
	 * @param registry the bean definition registry used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	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。

小结

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。

BeanFactoryPostProcessor原理

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.
			/**
			 * 准备上下文刷新工作，如设置初始值
			 */
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			/**
			 * 告诉子类刷新内部beanFactory，返回Bean工厂
			 */
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			/**
			 * 准备beanFactory，以便于上下文中使用
			 */
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				/**
				 * 允许在上下文子类中对bean工厂进行后处理。
				 */
				postProcessBeanFactory(beanFactory);

				/**
				 * 开启处理PostProcessors步骤器
				 */
				StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
				// Invoke factory processors registered as beans in the context.
				/**
				 * 调用BeanFactory的后置处理器
				 */
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				/**
				 *
				 * 注册拦截bean创建的bean处理器
				 */
				registerBeanPostProcessors(beanFactory);
				/**
				 * 处理PostProcessors步骤器
				 */
				beanPostProcess.end();

				// Initialize message source for this context.
				/**
				 * 初始化MessageSource
				 */
				initMessageSource();

				// Initialize event multicaster for this context.
				/**
				 * 初始化Application监听器的管理Bean（ApplicationEventMulticaster）
				 */
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				/**
				 * 模板模式，刷新Bean的操作，由子类实现具体逻辑
				 */
				onRefresh();

				// Check for listener beans and register them.
				/**
				 * 检查和注册监听器
				 */
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				/**
				 * 实例化所有（非惰性初始化）单例
				 */
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				/**
				 * 发布相应的事件
				 */
				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。

invokeBeanFactoryPostProcessors

	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		/**
		 * 执行BeanFactoryPostProcessor，是该方法的处理核心
		 */
		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)
		/**
		 * 检查和赋初始值
		 */
		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<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
		Set<String> processedBeans = new HashSet<>();

		/**
		 * 首先调用BeanDefinitionRegistryPostProcessors（如果有）。
		 */
		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			/**
			 * 用于存放BeanFactoryPostProcessor的对象
			 */
			List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
			/**
			 * 用户存放BeanDefinitionRegistryPostProcessor对象
			 */
			List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();


			/********************************* 下面处理BeanDefinitionRegistryPostProcessor逻辑 *************************************/


			/**
			 * 遍历最原始的BeanFactoryPostProcessor列表，找出BeanDefinitionRegistryPostProcessor和 BeanFactoryPostProcessor
			 * BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口
			 */
			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
					BeanDefinitionRegistryPostProcessor registryProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					/**
					 * 执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry
					 */
					registryProcessor.postProcessBeanDefinitionRegistry(registry);
					registryProcessors.add(registryProcessor);
				}
				else {
					regularPostProcessors.add(postProcessor);
				}
			}

			/**
			 * 定义当前找到的BeanDefinitionRegistryPostProcessor临时存储
			 */
			List<BeanDefinitionRegistryPostProcessor> 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();
			}

			/**
			 * 批量执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry
			 */
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			/**
			 * 批量执行BeanFactoryPostProcessor（最开始的BeanFactoryPostProcessor）
			 */
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		}

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

		/********************************* 下面处理BeanFactoryPostProcessor逻辑（可能执行上面步骤产生新的BeanFactoryPostProcessor），执行逻辑和BeanDefinitionRegistryPostProcessor一致 *************************************/

		// 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<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);
			}
		}

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

		// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
		List<BeanFactoryPostProcessor> 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<BeanFactoryPostProcessor> 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();
	}


	/**
	 * 排序BeanFactoryPostProcessor
	 * @param postProcessors
	 * @param beanFactory
	 */
	private static void sortPostProcessors(List<?> postProcessors, ConfigurableListableBeanFactory beanFactory) {
		// Nothing to sort?
		if (postProcessors.size() <= 1) {
			return;
		}
		Comparator<Object> comparatorToUse = null;
		if (beanFactory instanceof DefaultListableBeanFactory) {
			comparatorToUse = ((DefaultListableBeanFactory) beanFactory).getDependencyComparator();
		}
		if (comparatorToUse == null) {
			comparatorToUse = OrderComparator.INSTANCE;
		}
		postProcessors.sort(comparatorToUse);
	}


	/**
	 * 执行  BeanDefinitionRegistryPostProcessor
	 * @param postProcessors
	 * @param registry
	 * @param applicationStartup
	 */
	private static void invokeBeanDefinitionRegistryPostProcessors(
			Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {

		for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
			StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
					.tag("postProcessor", postProcessor::toString);
			postProcessor.postProcessBeanDefinitionRegistry(registry);
			postProcessBeanDefRegistry.end();
		}
	}


	/**
	 * 执行invokeBeanFactoryPostProcessors
	 * @param postProcessors
	 * @param beanFactory
	 */
	private static void invokeBeanFactoryPostProcessors(
			Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {

		for (BeanFactoryPostProcessor postProcessor : postProcessors) {
			StartupStep postProcessBeanFactory = beanFactory.getApplicationStartup().start("spring.context.bean-factory.post-process")
					.tag("postProcessor", postProcessor::toString);
			postProcessor.postProcessBeanFactory(beanFactory);
			postProcessBeanFactory.end();
		}
	}

	

上面是spring执行BeanFactoryPostProcessor的具体逻辑，执行流程非常清晰，执行步骤如下：

• 第一步 ：遍历最原始的BeanFactoryPostProcessor，找到BeanDefinitionRegistryPostProcessor和BeanFactoryPostProcessor，且执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry(registry)方法加载Bean。

• 第二步 ：从BeanFactory中寻找BeanDefinitionRegistryPostProcessor的PriorityOrdered（最高优先级的排序）类型Bean，排序后执行postProcessBeanDefinitionRegistry(registry)方法加载Bean。

• 第三步 ：从BeanFactory中寻找BeanDefinitionRegistryPostProcessor未被加载的Ordered（排序）类型Bean，排序后执行postProcessBeanDefinitionRegistry(registry)方法加载Bean。

• 第四步 ：从BeanFactory中寻找出未被加载的BeanDefinitionRegistryPostProcessor类型Bean，然后执行postProcessBeanDefinitionRegistry(registry)方法加载Bean，这一步目的就是处理加载新的BeanDefinitionRegistryPostProcessor的Bean。

• 第五步 ：从BeanFactory中寻找BeanFactoryPostProcessor的PriorityOrdered（最高优先级的排序）类型Bean，排序后执行postProcessBeanFactory(beanFactory)方法加载Bean。

• 第六步 ：从BeanFactory中寻找BeanFactoryPostProcessor未被加载的Ordered（排序）的类型Bean，排序后执行postProcessBeanFactory(beanFactory)方法加载Bean。

• 第七步 ：从BeanFactory中寻找出未排序的BeanFactoryPostProcessor类型Bean，然后执行postProcessBeanFactory(beanFactory)方法加载Bean。

总结

BeanFactoryPostProcessor是执行最早的后置处理器，了解其原理对我们开发spring插件有很大的帮助，特别是BeanDefinitionRegistryPostProcessor接口对外扩展spring加载Bean的多样化。希望通过源码的角度帮助读者知其然更知其所以然。