Spring源码之BeanFactoryPostProcessor(后置处理器)。
有点程度的Spring开发人员想必都晓得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，实现这个接口能够在beanFactory初始化前做一些事。
咱们熟知的Spring和Mybatis的联合，正是因为Mybatis实现了BeanFactoryPostProcessor，它的重要性显而易见，深刻了解他对于切入Mybatis源码有着粗浅的意义。
如下图是简略的利用：
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、刷新前的筹备 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，增加几个 BeanPostProcessor，手动注册几个非凡的 bean prepareBeanFactory(beanFactory); try { //4、模板办法 // 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、模板办法--springboot实现了这个办法 onRefresh(); // Check for listener beans and register them. //7、注册监听器 registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. //8、实现bean工厂的初始化**办法********************************************** 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 Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }benafactory源码的解决位于第三个地位。
次要波及到两个办法postProcessBeanFactory(beanFactory);
和invokeBeanFactoryPostProcessors(beanFactory);
postProcessBeanFactory(beanFactory)点进去发现是一个空办法，具体的执行在invokeBeanFactoryPostProcessors(beanFactory);中
咱们在invokeBeanFactoryPostProcessors办法上打断点一探到底。第一次看的时候感觉这是什么玩意，这么长，耐住性子一步步的往下看。
办法虽长大略总结一下就是，判断beanFactory类型，而后将注册的BeanPostFactory放入、排好程序、执行。
invokeBeanFactoryPostProcessors 办法的内容其实比拟少，大部分过程在正文都曾经写分明，这边在略微总结一下。
整个 invokeBeanFactoryPostProcessors 办法围绕两个接口，BeanDefinitionRegistryPostProcessor 和 BeanFactoryPostProcessor，其中 BeanDefinitionRegistryPostProcessor 继承了 BeanFactoryPostProcessor 。
BeanDefinitionRegistryPostProcessor 次要用来在惯例 BeanFactoryPostProcessor 检测开始之前注册其余 Bean 定义，说的简略点，就是 BeanDefinitionRegistryPostProcessor 具备更高的优先级，执行程序在 BeanFactoryPostProcessor 之前。
具体的过程看正文吧
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，因而这边为true if (beanFactory instanceof BeanDefinitionRegistry) { BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; // 用于寄存一般的BeanFactoryPostProcessor List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>(); // 用于寄存BeanDefinitionRegistryPostProcessor List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>(); // 2.首先解决入参中的beanFactoryPostProcessors // 遍历所有的beanFactoryPostProcessors, 将BeanDefinitionRegistryPostProcessor和一般BeanFactoryPostProcessor辨别开 for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { // 2.1 如果是BeanDefinitionRegistryPostProcessor BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; // 2.1.1 间接执行BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry办法 registryProcessor.postProcessBeanDefinitionRegistry(registry); // 2.1.2 增加到registryProcessors(用于最初执行postProcessBeanFactory办法) registryProcessors.add(registryProcessor); } else { // 2.2 否则，只是一般的BeanFactoryPostProcessor // 2.2.1 增加到regularPostProcessors(用于最初执行postProcessBeanFactory办法) 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. // 用于保留本次要执行的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, 增加到currentRegistryProcessors中, currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); // 3.5 将要被执行的退出processedBeans，防止后续反复执行 processedBeans.add(ppName); } } // 3.6 进行排序(依据是否实现PriorityOrdered、Ordered接口和order值来排序) sortPostProcessors(currentRegistryProcessors, beanFactory); // 3.7 增加到registryProcessors(用于最初执行postProcessBeanFactory办法) registryProcessors.addAll(currentRegistryProcessors); // 3.8 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry办法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); // 3.9 执行结束后, 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（过程跟下面的步骤3根本一样） // 4.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的类, 这边反复查找是因为执行完下面的BeanDefinitionRegistryPostProcessor, // 可能会新增了其余的BeanDefinitionRegistryPostProcessor, 因而须要从新查找 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办法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear. // 5.最初, 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 跳过曾经执行过的 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, // 因而这边将reiterate赋值为true, 代表须要再循环查找一次 reiterate = true; } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); // 5.4 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry办法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); } // Now, invoke the postProcessBeanFactory callback of all processors handled so far. // 6.调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory办法(BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor) invokeBeanFactoryPostProcessors(registryProcessors, beanFactory); // 7.最初, 调用入参beanFactoryPostProcessors中的一般BeanFactoryPostProcessor的postProcessBeanFactory办法 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曾经全副处理完毕, // 上面开始解决容器中的所有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. // 用于寄存实现了PriorityOrdered接口的BeanFactoryPostProcessor List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); // 用于寄存实现了Ordered接口的BeanFactoryPostProcessor的beanName List<String> orderedPostProcessorNames = new ArrayList<>(); // 用于寄存一般BeanFactoryPostProcessor的beanName List<String> nonOrderedPostProcessorNames = new ArrayList<>(); // 8.1 遍历postProcessorNames, 将BeanFactoryPostProcessor按实现PriorityOrdered、实现Ordered接口、一般三种辨别开 for (String ppName : postProcessorNames) { // 8.2 跳过曾经执行过的 if (processedBeans.contains(ppName)) { // skip - already processed in first phase above } else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { // 8.3 增加实现了PriorityOrdered接口的BeanFactoryPostProcessor priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class)); } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { // 8.4 增加实现了Ordered接口的BeanFactoryPostProcessor的beanName orderedPostProcessorNames.add(ppName); } else { // 8.5 增加剩下的一般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办法 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, 增加到orderedPostProcessors, 筹备执行 orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } // 10.2 对orderedPostProcessors排序 sortPostProcessors(orderedPostProcessors, beanFactory); // 10.3 遍历orderedPostProcessors, 执行postProcessBeanFactory办法 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, 增加到nonOrderedPostProcessors, 筹备执行 nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } // 11.2 遍历nonOrderedPostProcessors, 执行postProcessBeanFactory办法 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.革除元数据缓存（mergedBeanDefinitions、allBeanNamesByType、singletonBeanNamesByType）， // 因为后处理器可能曾经批改了原始元数据，例如， 替换值中的占位符... beanFactory.clearMetadataCache(); }