整体流程
源码理解
源码位于PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors方法，这里省略了上下文，需要知道该方法是在BeanFactory准备完成后调用，位置如下图所示：
关于代码的理解都写在注释中：
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// WARNING: Although it may appear that the body of this method can be easily
// refactored to avoid the use of multiple loops and multiple lists, the use
// of multiple lists and multiple passes over the names of processors is
// intentional. We must ensure that we honor the contracts for PriorityOrdered
// and Ordered processors. Specifically, we must NOT cause processors to be
// instantiated (via getBean() invocations) or registered in the ApplicationContext
// in the wrong order.
//
// Before submitting a pull request (PR) to change this method, please review the
// list of all declined PRs involving changes to PostProcessorRegistrationDelegate
// to ensure that your proposal does not result in a breaking change:
// https://github.com/spring-projects/spring-framework/issues?q=PostProcessorRegistrationDelegate+is%3Aclosed+label%3A%22status%3A+declined%22
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
// 无论什么情况，优先执行BeanDefinitionRegistryPostProcessors
// 将已经执行过的BFPP存储在processedBeans中，防止重复执行
Set<String> processedBeans = new HashSet<>();
// 判断beanFactory是否是BeanDefinitionRegistry类型，此处是DefaultListableBeanFactory，实现了BeanDefinitionRegistry接口，所以是true
if (beanFactory instanceof BeanDefinitionRegistry registry) {
// BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子集
// BeanDefinitionRegistryPostProcessor主要针对对象是BeanDefinition，BeanFactoryPostProcessor主要针对对象是BeanFactory
// 存放BeanFactoryPostProcessor的集合
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// 存放BeanDefinitionRegistryPostProcessor的集合
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
// 1. 先处理外部集合传入的beanFactoryPostProcessors
// 将BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor区分开
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor registryProcessor) {
// 直接执行下面方法
registryProcessor.postProcessBeanDefinitionRegistry(registry);
// 添加到registryProcessors集合中，后续会执行postProcessBeanFactory方法
registryProcessors.add(registryProcessor);
}
else {
// 添加到regularPostProcessors集合中，后续会执行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.
// 保存本次要执行的BeanDefinitionRegistryPostProcessors
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
// 2. 调用所有实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessor实现类
// 找到所有实现BeanDefinitionRegistryPostProcessor接口的bean的name
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
// 遍历处理所有符合规则的postProcessorNames
for (String ppName : postProcessorNames) {
// 检查是否实现了PriorityOrdered接口
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
// 获取名字对应的bean实例，添加到currentRegistryProcessors中
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
// 将要被执行的BFPP名称添加到processedBeans中，避免后续重复执行
processedBeans.add(ppName);
}
}
// 按照优先级进行排序操作
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 添加到registryProcessors中，用于最后执行postProcessBeanFactory方法
// 前面第一步添加的是外部定义的BeanDefinitionRegistryPostProcessor，这一步将有排序的添加进去
registryProcessors.addAll(currentRegistryProcessors);
// 遍历currentRegistryProcessors，执行postProcessBeanDefinitionRegistry方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
// 执行完毕后清空currentRegistryProcessors
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
// 3. 调用所有实现Ordered接口的BeanDefinitionRegistryPostProcessors实现类
// 找到所有实现BeanDefinitionRegistryPostProcessor接口的bean的name
// 为什么和第2步重复？因为在上面执行过程中可能会新增其他的BeanDefinitionRegistryPostProcessor
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 检查是否实现了Ordered接口，并且还未执行过
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
// 获取名字对应的bean实例，添加到currentRegistryProcessors中
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
// 将要被执行的BFPP名称添加到processedBeans中，避免后续重复执行
processedBeans.add(ppName);
}
}
// 按照优先级进行排序操作
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 添加到registryProcessors中，用于最后执行postProcessBeanFactory方法
registryProcessors.addAll(currentRegistryProcessors);
// 遍历currentRegistryProcessors，执行postProcessBeanDefinitionRegistry方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
// 执行完毕后清空currentRegistryProcessors
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 最后，调用剩下的BeanDefinitionRegistryPostProcessor
boolean reiterate = true;
while (reiterate) {
reiterate = false;
// 找到所有实现BeanDefinitionRegistryPostProcessor接口的bean的name
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 跳过已经执行过的
if (!processedBeans.contains(ppName)) {
// 获取名字对应的bean实例，添加到currentRegistryProcessors中
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
// 将要被执行的BFPP名称添加到processedBeans中，避免后续重复执行
processedBeans.add(ppName);
// 这里为true的原因是：
// 如果还有未处理的，下面会进行处理逻辑，在执行过程中很可能会再产生BeanDefinitionRegistryPostProcessor
reiterate = true;
}
}
// 按照优先级进行排序操作
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 添加到registryProcessors中，用于最后执行postProcessBeanFactory方法
registryProcessors.addAll(currentRegistryProcessors);
// 遍历currentRegistryProcessors，执行postProcessBeanDefinitionRegistry方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
// 执行完毕后清空currentRegistryProcessors
currentRegistryProcessors.clear();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
// 调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法
// 因为实现了BeanDefinitionRegistryPostProcessor接口一定也实现了BeanFactoryPostProcessor接口
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
// 调用入参beanFactoryPostProcessors中所有普通BeanFactoryPostProcessor的postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
// 如果beanFactory不属于BeanDefinitionRegistry类型，直接执行postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// 到此为止，入参beanFactoryPostProcessors和容器中所有的BeanDefinitionRegistryPostProcessors已经全部处理完毕，
// 下面开始处理容器中通过@Component注解提供的BeanFactoryPostProcessor，而不是ac.addBeanFactoryPostProcessor提供的
// 上面执行的，仅仅是程序员通过add到spring容器中的beanFactoryPostProcessor
// 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.
// 用于存放实现了PriorityOrdered接口BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// 用于存放实现了Ordered接口BeanFactoryPostProcessor的name
List<String> orderedPostProcessorNames = new ArrayList<>();
// 用于存放普通BeanFactoryPostProcessor的name
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 遍历postProcessorNames，将实现的PriorityOrdered接口、rdered接口、普通三种区别开
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.
// 对实现PriorityOrdered接口的BeanFactoryPostProcessor进行排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 遍历实现PriorityOrdered接口的BeanFactoryPostProcessor，执行postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
// 创建存放Ordered接口的集合
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
// 将实现Ordered接口的BeanFactoryPostProcessor添加到集合中
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
// 对实现Ordered接口的BeanFactoryPostProcessor进行排序
sortPostProcessors(orderedPostProcessors, beanFactory);
// 遍历实现Ordered接口的BeanFactoryPostProcessor，执行postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
// 创建存放普通对象的集合
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
for (String postProcessorName : nonOrderedPostProcessorNames) {
// 将普通的BeanFactoryPostProcessor添加到集合中
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
// 遍历普通的BeanFactoryPostProcessor，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...
// 清除元数据缓存（mergeBeanDefinitions、allBeanNamesByType、singletonBeanNameByType）
// 因为后置处理器可能已经修改了原始数据，比如：替换值中的占位符
beanFactory.clearMetadataCache();
}
