Spring的BeanFactoryPostProcessor接口

接口简介

BeanFactoryPostProcessor 接口是 Spring 初始化 BeanFactory 时对外暴露的扩展点,Spring IoC 容器允许 BeanFactoryPostProcessor 在容器实例化任何 bean 之前读取 bean 的定义,并可以修改它。

BeanDefinitionRegistryPostProcessor 继承自 BeanFactoryPostProcessor,比 BeanFactoryPostProcessor 具有更高的优先级,主要用来在常规的 BeanFactoryPostProcessor 检测开始之前注册其他 bean 定义。特别是,你可以通过 BeanDefinitionRegistryPostProcessor 来注册一些常规的 BeanFactoryPostProcessor,因为此时所有常规的 BeanFactoryPostProcessor 都还没开始被处理。

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注意点:通过BeanDefinitionRegistryPostProcessor 注册的 BeanDefinitionRegistryPostProcessor 接口的postProcessBeanDefinitionRegistry方法将得不到调用,具体的原因会在下面的代码中解释。

BeanFactoryPostProcessor 接口调用机制

BeanFactoryPostProcessor 接口的调用在 AbstractApplicationContext#invokeBeanFactoryPostProcessors方法中。

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()));
		}
	}

进入PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors())方法:

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

简单总结

上面的方法看起来很长很复杂,但其实干的事情并不多,就调用了BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor接口的实现。这边再简单总结下具体的过程:

step1:执行通过ApplicationContext#addBeanFactoryPostProcessor()方法注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor。

具体过程如下:假如通过ApplicationContext注册了一个BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor,那么会先执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法,但是BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法和BeanFactoryPostProcessor的postProcessBeanFactory方法暂时都不会在这步执行。

另外需要注意的是:通过ApplicationContext注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor都不支持@PriorityOrdered和@Ordered顺序处理,而是按照我们添加的顺序处理

step2:处理BeanFactory中的BeanDefinitionRegistryPostProcessor,处理的顺序是先处理@PriorityOrdered标注的,再处理@Ordered标注的,最后处理普通的BeanDefinitionRegistryPostProcessor。到这边,所有BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry方法都已经调用完毕,下面就开始处理BeanFactoryPostProcessor的postProcessBeanFactory方法。

step3:调用BeanDefinitionRegistryPostProcessor实现的postProcessBeanFactory方法(因为BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口)

step4:调用通过ApplicationContext#addBeanFactoryPostProcessor()注册的“单纯”的BeanFactoryPostProcessor

step5:调用BeanFactory中的BeanFactoryPostProcessor,调用顺序也是按照@PriorityOrdered和@Ordered顺序处理,没有这两个注解的最后处理。

好了,到这边BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor接口就已经处理完了。后面我们会拿ConfigurationClassPostProcessor 这个特殊的BeanDefinitionRegistryPostProcessor做列子讲下具体流程,这边只是介绍BeanFactoryPostProcessor的调用机制。

posted @ 2021-02-24 13:50  程序员自由之路  阅读(236)  评论(0编辑  收藏