Spring源码之BeanFactoryPostProcessor(后置处理器) _Spring源码

满堂花醉三千客，一剑霜寒十四洲。这篇文章主要讲述Spring源码之BeanFactoryPostProcessor(后置处理器)相关的知识，希望能为你提供帮助。
Spring源码之BeanFactoryPostProcessor(后置处理器)。
有点水平的Spring开发人员想必都知道BeanFactoryPostProcessor也就是常说的后置管理器，这是Spirng生命周期中的一个接口，实现这个接口可以在beanFactory初始化前做一些事。
【Spring源码之BeanFactoryPostProcessor(后置处理器)】我们熟知的Spring和Mybatis的结合，正是因为Mybatis实现了BeanFactoryPostProcessor，它的重要性不言而喻，深入理解他对于切入Mybatis源码有着深刻的意义。
如下图是简单的应用：

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还是先贴上refresh()的源码

@Override public void refresh() throws BeansException, IllegalStateException synchronized (this.startupShutdownMonitor) // Prepare this context for refreshing. //1、刷新前的准备 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. //2、将会初始化 BeanFactory、加载 Bean、注册 Bean ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. //3、设置 BeanFactory 的类加载器，添加几个 BeanPostProcessor，手动注册几个特殊的 bean prepareBeanFactory(beanFactory); try //4、模板方法 // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. //执行BeanFactory后置处理器 invokeBeanFactoryPostProcessors(beanFactory); // 5、Register bean processors that intercept bean creation. //注册bean后置处理器 registerBeanPostProcessors(beanFactory); // Initialize message source for this context. //国际化 initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. //6、模板方法--springboot实现了这个方法 onRefresh(); // Check for listener beans and register them. //7、注册监听器 registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. //8、完成bean工厂的初始化**方法********************************************** finishBeanFactoryInitialization(beanFactory); //9、 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 Springs core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches();

benafactory源码的处理位于第三个位置。
主要涉及到两个方法postProcessBeanFactory(beanFactory);
和invokeBeanFactoryPostProcessors(beanFactory);

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postProcessBeanFactory(beanFactory)点进去发现是一个空方法，具体的执行在invokeBeanFactoryPostProcessors(beanFactory); 中

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我们在invokeBeanFactoryPostProcessors方法上打断点一探究竟。第一次看的时候觉得这是什么玩意，这么长，耐住性子一步步的往下看。
方法虽长大概总结一下就是，判断beanFactory类型，然后将注册的BeanPostFactory放入、排好顺序、执行。
invokeBeanFactoryPostProcessors 方法的内容其实比较少，大部分过程在注释都已经写清楚，这边在稍微总结一下。
整个 invokeBeanFactoryPostProcessors 方法围绕两个接口，BeanDefinitionRegistryPostProcessor 和 BeanFactoryPostProcessor，其中 BeanDefinitionRegistryPostProcessor 继承了 BeanFactoryPostProcessor 。
BeanDefinitionRegistryPostProcessor 主要用来在常规 BeanFactoryPostProcessor 检测开始之前注册其他 Bean 定义，说的简单点，就是 BeanDefinitionRegistryPostProcessor 具有更高的优先级，执行顺序在 BeanFactoryPostProcessor 之前。
具体的过程看注释吧

public static void invokeBeanFactoryPostProcessors( ConfigurableListableBeanFactory beanFactory, List< BeanFactoryPostProcessor> beanFactoryPostProcessors) // Invoke BeanDefinitionRegistryPostProcessors first, if any. Set< String> processedBeans = new HashSet< > (); // 1.判断beanFactory是否为BeanDefinitionRegistry，beanFactory为DefaultListableBeanFactory, // 而DefaultListableBeanFactory实现了BeanDefinitionRegistry接口，因此这边为true if (beanFactory instanceof BeanDefinitionRegistry) BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; // 用于存放普通的BeanFactoryPostProcessor List< BeanFactoryPostProcessor> regularPostProcessors = new ArrayList< > (); // 用于存放BeanDefinitionRegistryPostProcessor List< BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList< > (); // 2.首先处理入参中的beanFactoryPostProcessors // 遍历所有的beanFactoryPostProcessors, 将BeanDefinitionRegistryPostProcessor和普通BeanFactoryPostProcessor区分开 for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) // 2.1 如果是BeanDefinitionRegistryPostProcessor BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; // 2.1.1 直接执行BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry方法 registryProcessor.postProcessBeanDefinitionRegistry(registry); // 2.1.2 添加到registryProcessors(用于最后执行postProcessBeanFactory方法) registryProcessors.add(registryProcessor); else // 2.2 否则，只是普通的BeanFactoryPostProcessor // 2.2.1 添加到regularPostProcessors(用于最后执行postProcessBeanFactory方法) regularPostProcessors.add(postProcessor); // Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let the bean factory post-processors apply to them! // Separate between BeanDefinitionRegistryPostProcessors that implement // PriorityOrdered, Ordered, and the rest. // 用于保存本次要执行的BeanDefinitionRegistryPostProcessor List< BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList< > (); // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered. // 3.调用所有实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessor实现类 // 3.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的Bean的beanName String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); // 3.2 遍历postProcessorNames for (String ppName : postProcessorNames) // 3.3 校验是否实现了PriorityOrdered接口 if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) // 3.4 获取ppName对应的bean实例, 添加到currentRegistryProcessors中, currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); // 3.5 将要被执行的加入processedBeans，避免后续重复执行 processedBeans.add(ppName); // 3.6 进行排序(根据是否实现PriorityOrdered、Ordered接口和order值来排序) sortPostProcessors(currentRegistryProcessors, beanFactory); // 3.7 添加到registryProcessors(用于最后执行postProcessBeanFactory方法) registryProcessors.addAll(currentRegistryProcessors); // 3.8 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); // 3.9 执行完毕后, 清空currentRegistryProcessors currentRegistryProcessors.clear(); // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered. // 4.调用所有实现了Ordered接口的BeanDefinitionRegistryPostProcessor实现类（过程跟上面的步骤3基本一样） // 4.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的类, 这边重复查找是因为执行完上面的BeanDefinitionRegistryPostProcessor, // 可能会新增了其他的BeanDefinitionRegistryPostProcessor, 因此需要重新查找 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) // 校验是否实现了Ordered接口，并且还未执行过 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); // 4.2 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear. // 5.最后, 调用所有剩下的BeanDefinitionRegistryPostProcessors boolean reiterate = true; while (reiterate) reiterate = false; // 5.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的类 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) // 5.2 跳过已经执行过的 if (!processedBeans.contains(ppName)) currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); // 5.3 如果有BeanDefinitionRegistryPostProcessor被执行, 则有可能会产生新的BeanDefinitionRegistryPostProcessor, // 因此这边将reiterate赋值为true, 代表需要再循环查找一次 reiterate = true; sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); // 5.4 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); // Now, invoke the postProcessBeanFactory callback of all processors handled so far. // 6.调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法(BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor) invokeBeanFactoryPostProcessors(registryProcessors, beanFactory); // 7.最后, 调用入参beanFactoryPostProcessors中的普通BeanFactoryPostProcessor的postProcessBeanFactory方法 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! // 到这里 , 入参beanFactoryPostProcessors和容器中的所有BeanDefinitionRegistryPostProcessor已经全部处理完毕, // 下面开始处理容器中的所有BeanFactoryPostProcessor// Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let the bean factory post-processors apply to them! // 8.找出所有实现BeanFactoryPostProcessor接口的类 String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false); // Separate between BeanFactoryPostProcessors that implement PriorityOrdered, // Ordered, and the rest. // 用于存放实现了PriorityOrdered接口的BeanFactoryPostProcessor List< BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList< > (); // 用于存放实现了Ordered接口的BeanFactoryPostProcessor的beanName List< String> orderedPostProcessorNames = new ArrayList< > (); // 用于存放普通BeanFactoryPostProcessor的beanName List< String> nonOrderedPostProcessorNames = new ArrayList< > (); // 8.1 遍历postProcessorNames, 将BeanFactoryPostProcessor按实现PriorityOrdered、实现Ordered接口、普通三种区分开 for (String ppName : postProcessorNames) // 8.2 跳过已经执行过的 if (processedBeans.contains(ppName)) // skip - already processed in first phase aboveelse if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) // 8.3 添加实现了PriorityOrdered接口的BeanFactoryPostProcessor priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class)); else if (beanFactory.isTypeMatch(ppName, Ordered.class)) // 8.4 添加实现了Ordered接口的BeanFactoryPostProcessor的beanName orderedPostProcessorNames.add(ppName); else // 8.5 添加剩下的普通BeanFactoryPostProcessor的beanName nonOrderedPostProcessorNames.add(ppName); // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered. // 9.调用所有实现PriorityOrdered接口的BeanFactoryPostProcessor // 9.1 对priorityOrderedPostProcessors排序 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); // 9.2 遍历priorityOrderedPostProcessors, 执行postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); // Next, invoke the BeanFactoryPostProcessors that implement Ordered. // 10.调用所有实现Ordered接口的BeanFactoryPostProcessor List< BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList< > (); for (String postProcessorName : orderedPostProcessorNames) // 10.1 获取postProcessorName对应的bean实例, 添加到orderedPostProcessors, 准备执行 orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); // 10.2 对orderedPostProcessors排序 sortPostProcessors(orderedPostProcessors, beanFactory); // 10.3 遍历orderedPostProcessors, 执行postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); // Finally, invoke all other BeanFactoryPostProcessors. // 11.调用所有剩下的BeanFactoryPostProcessor List< BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList< > (); for (String postProcessorName : nonOrderedPostProcessorNames) // 11.1 获取postProcessorName对应的bean实例, 添加到nonOrderedPostProcessors, 准备执行 nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); // 11.2 遍历nonOrderedPostProcessors, 执行postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory); // Clear cached merged bean definitions since the post-processors might have // modified the original metadata, e.g. replacing placeholders in values... // 12.清除元数据缓存（mergedBeanDefinitions、allBeanNamesByType、singletonBeanNamesByType）， // 因为后处理器可能已经修改了原始元数据，例如，替换值中的占位符... beanFactory.clearMetadataCache();