Sping源码（七）— 后置处理器

简单回顾一下上一篇文章，是在BeanFacroty创建完之后，可以通过Editor和EditorRegistrar实现对类属性的自定义扩展，以及忽略要自动装配的Aware接口。
本篇帖子会顺着refresh()主流程方法接着向下执行。在讲invokeBeanFactoryPostProcessors方法的具体逻辑之前，先简单介绍BeanFactoryPostProcessor接口和整个invokeBeanFactoryPostProcessors方法的执行流程。

refresh

public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// Prepare this context for refreshing./*** 前戏，做容器刷新前的准备工作* 1、设置容器的启动时间* 2、设置活跃状态为true* 3、设置关闭状态为false* 4、获取Environment对象，并加载当前系统的属性值到Environment对象中* 5、准备监听器和事件的集合对象，默认为空的集合*/prepareRefresh();// Tell the subclass to refresh the internal bean factory.// 创建容器对象：DefaultListableBeanFactory// 加载xml配置文件的属性值到当前工厂中，最重要的就是BeanDefinitionConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// Prepare the bean factory for use in this context.// beanFactory的准备工作，对各种属性进行填充prepareBeanFactory(beanFactory);try {// Allows post-processing of the bean factory in context subclasses.// 子类覆盖方法做额外的处理，此处我们自己一般不做任何扩展工作，但是可以查看web中的代码，是有具体实现的postProcessBeanFactory(beanFactory);// Invoke factory processors registered as beans in the context.// 调用各种beanFactory处理器invokeBeanFactoryPostProcessors(beanFactory);}		}}

@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;
}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;
}

BFPP和BDRPP

根据上面的流程图以及代码块可以看出BFPP和BDRPP的关系，其中BFPP类中只有一个postProcessBeanFactory()方法，而BDRPP中只有postProcessBeanDefinitionRegistry()方法，因为是继承的关系，所以所有实现BDRPP接口的类，也会有postProcessBeanFactory()方法。
而BFPP和BDRPP其中有一个很重要的区别就在于，它们两个方法接收的参数不同，其中BFPP接收BeanFactory参数，针对整个BeanFactory做操作，而BDRPP接收的参数是BeanDefinitionRegistry（可以理解是对Definition做一些正删改查的操作）。

BeanDefinitionRegistry

public interface BeanDefinitionRegistry extends AliasRegistry {/*** 注册BeanDefinition到注册表** Register a new bean definition with this registry.* Must support RootBeanDefinition and ChildBeanDefinition.* @param beanName the name of the bean instance to register* @param beanDefinition definition of the bean instance to register* @throws BeanDefinitionStoreException if the BeanDefinition is invalid* @throws BeanDefinitionOverrideException if there is already a BeanDefinition* for the specified bean name and we are not allowed to override it* @see GenericBeanDefinition* @see RootBeanDefinition* @see ChildBeanDefinition*/void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)throws BeanDefinitionStoreException;/*** 移除注册表中beanName的BeanDefinition** Remove the BeanDefinition for the given name.* @param beanName the name of the bean instance to register* @throws NoSuchBeanDefinitionException if there is no such bean definition*/void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;/*** 获取注册表中beanName的BeanDefinition** Return the BeanDefinition for the given bean name.* @param beanName name of the bean to find a definition for* @return the BeanDefinition for the given name (never {@code null})* @throws NoSuchBeanDefinitionException if there is no such bean definition*/BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;/*** 检查此注册表是否包含具有给定名称的BeanDefinition** Check if this registry contains a bean definition with the given name.* @param beanName the name of the bean to look for* @return if this registry contains a bean definition with the given name*/boolean containsBeanDefinition(String beanName);/*** 返回此注册表中定义的所有bean的名称** Return the names of all beans defined in this registry.* @return the names of all beans defined in this registry,* or an empty array if none defined*/String[] getBeanDefinitionNames();/*** 返回注册表中定义的bean的数目** Return the number of beans defined in the registry.* @return the number of beans defined in the registry*/int getBeanDefinitionCount();/***  确定给定bean名称是否已在该注册表中使用** Determine whether the given bean name is already in use within this registry,* i.e. whether there is a local bean or alias registered under this name.* @param beanName the name to check* @return whether the given bean name is already in use*/boolean isBeanNameInUse(String beanName);}

接口的作用和整体的执行流程已经介绍完成，下面看看invokeBeanFactoryPostProcessors方法的具体执行逻辑。

invokeBeanFactoryPostProcessors

主要是调用delegate中的同名invokeBeanFactoryPostProcessors方法，对BaenFactory中和自定义注册进来的BFPP的实现类进行处理。
其中getBeanFactoryPostProcessors()是如果类继承了AbstractApplicationContext后，可以有add方法自行注册BeanFactoryPostProcessor。处理时也会先处理这部分的BFPP。

invokeBeanFactoryPostProcessors

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {// 获取到当前应用程序上下文的beanFactoryPostProcessors变量的值，并且实例化调用执行所有已经注册的beanFactoryPostProcessor// 默认情况下，通过getBeanFactoryPostProcessors()来获取已经注册的BFPP，但是默认是空的PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantimeif (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));}}

AbstractApplicationContext
如果想要自己注册进来，要实现AbstractApplicationContext并调用addBeanFactoryPostProcessor方法将自定义BFPP实现类加进来，就可以get到。

public abstract class AbstractApplicationContext extends DefaultResourceLoaderimplements ConfigurableApplicationContext {@Overridepublic void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor) {this.beanFactoryPostProcessors.add(postProcessor);}/*** Return the list of BeanFactoryPostProcessors that will get applied* to the internal BeanFactory.*/public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {return this.beanFactoryPostProcessors;}//删除其他代码
}	

具体处理逻辑
如最开始图片中标注的处理流程一样，

1. 处理过的BFPP都放入processedBeans集合，避免后续重复执行。
2. 先遍历beanFactoryPostProcessors中BDRPP类型的，并直接调用postProcessBeanDefinitionRegistry进行逻辑处理。非BDRPP类型放入regularPostProcessors集合，后续统一处理。
3. 找到BeanFactory中BDRPP类型，并根据PriorityOrdered，Order进行优先级排序，最后再执行没有优先级的。
4. 因为继承了BDRPP的肯定也会有BFPP中的方法，所以还会统一处理执行BDRPP中的postProcessBeanFactory方法。
5. 执行完BeanFactory中的BDRPP类型后，再查找BeanFactory中BFPP类型，同样按照PriorityOrdered，Order进行优先级排序。并执行postProcessBeanFactory方法。

class PostProcessorRegistrationDelegate {public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {// Invoke BeanDefinitionRegistryPostProcessors first, if any.//所有已经执行过BFPP的存储在processedBeans，防止重复执行Set<String> processedBeans = new HashSet<String>();//判断beanFactory是否属于BeanDefinitionRegistry类型，默认的beanFactory是DefaultListableBeanFactory，//实现了BeanDefinitionRegistry 所以为trueif (beanFactory instanceof BeanDefinitionRegistry) {//强制类型转换BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;//存放BFPP类型的集合List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();//存放BDRPP类型的集合List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =new LinkedList<BeanDefinitionRegistryPostProcessor>();//优先处理入参中的beanFactoryPostProcessors,遍历所有beanFactoryPostProcessors，//并将参数中的BFPP和BDRPP区分开for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {//如果是BDRPP类型if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {BeanDefinitionRegistryPostProcessor registryPostProcessor =(BeanDefinitionRegistryPostProcessor) postProcessor;//直接调用BDRPP中的postProcessBeanDefinitionRegistry具体方法进行处理registryPostProcessor.postProcessBeanDefinitionRegistry(registry);//放入registryPostProcessors集合中registryPostProcessors.add(registryPostProcessor);}else {//否则，只是普通的BeanFactoryPostProcessor，则放入regularPostProcessors集合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.//根据type获取BeanFactory中所有类型为BDRPP的postProcessorNamesString[] postProcessorNames =beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.//将实现了BDRPP和priorityOrder接口的类放入该集合List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();for (String ppName : postProcessorNames) {//如果是PriorityOrdered类型的if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {//放入priorityOrderedPostProcessors集合priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));//放入processedBeans集合，避免重复执行processedBeans.add(ppName);}}//按照优先级进行排序OrderComparator.sort(priorityOrderedPostProcessors);//添加到registryPostProcessors中registryPostProcessors.addAll(priorityOrderedPostProcessors);//遍历priorityOrderedPostProcessors集合，执行postProcessBeanDefinitionRegistry方法invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.//再次获取BDRPP类型的所有postProcessorNamespostProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);//实现了Order接口的BeanDefinitionRegistryPostProcessor放入该集合List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();for (String ppName : postProcessorNames) {//如果是没执行过，并且实现了Order接口的if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {//放到Order集合中orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));//放入processedBeans集合，避免重复执行processedBeans.add(ppName);}}//按照优先级排序OrderComparator.sort(orderedPostProcessors);//放入registryPostProcessors集合registryPostProcessors.addAll(orderedPostProcessors);//遍历orderedPostProcessors集合，执行postProcessBeanDefinitionRegistry方法invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.boolean reiterate = true;while (reiterate) {reiterate = false;//找出所有实现了BDRPP接口的类postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);for (String ppName : postProcessorNames) {//跳过执行过BDRPP的类if (!processedBeans.contains(ppName)) {//根据name获取实例BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);//添加到registryPostProcessors集合中registryPostProcessors.add(pp);//添加到processedBeans集合中processedBeans.add(ppName);//直接执行BDRPPpp.postProcessBeanDefinitionRegistry(registry);reiterate = true;}}}   // Now, invoke the postProcessBeanFactory callback of all processors handled so far.//遍历registryPostProcessors和regularPostProcessors中有所的bean，//执行BFPP接口postProcessBeanFactory方法invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);}//如果beanFactory不属于BeanDefinitionRegistry，直接执行具体方法else {// Invoke factory processors registered with the context instance.invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);}//到这为止，入参的beanFactoryPostProcessors和BeanFactory中BDRPP类型的方法已经全部处理完成//后面开始都是操作BFPP类型//到这位置// Do not initialize FactoryBeans here: We need to leave all regular beans// uninitialized to let the bean factory post-processors apply to them!//找到所有实现BeanFactoryPostProcessor的类String[] postProcessorNames =beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,// Ordered, and the rest.//依次声明priorityOrderedPostProcessors、orderedPostProcessorNames和nonOrderedPostProcessorNames分别用来存放对应//实现了priorityOrdered、ordered和没实现排序接口的类List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();List<String> orderedPostProcessorNames = new ArrayList<String>();List<String> nonOrderedPostProcessorNames = new ArrayList<String>();//遍历所有postProcessorNames，将没执行过的BFPP方法的类放入对应集合中。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.//按照优先级进行排序，并执行具体的BFPP方法OrderComparator.sort(priorityOrderedPostProcessors);invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);// Next, invoke the BeanFactoryPostProcessors that implement Ordered.List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();for (String postProcessorName : orderedPostProcessorNames) {orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}OrderComparator.sort(orderedPostProcessors);invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);// Finally, invoke all other BeanFactoryPostProcessors.List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();for (String postProcessorName : nonOrderedPostProcessorNames) {nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);}

看完上面这段源码之后，不知道大家有没有这样的一个疑问，为什么重复代码较多？每次都要根据类型重新获取String[] postProcessorNames，第一次获取后，根据postProcessorNames按照PriorityOrdered和Order进行优先级排序、分组执行不行么？
是因为在执行BDRPP的方法postProcessBeanDefinitionRegistry时，有可能会有新增的额外的BDRPP的类，每次都重新获取，能避免BDRPP类执行的不完全。