一 概述
invokeBeanFactoryPostProcessor主要作用是实例化已经在容器中注册过的BeanFactoryPostProcessor接口的实现类，回调postProcessBeanFactory方法等。
invokeBeanFactoryPostProcessor源码调用链又长又复杂，容易把人绕晕，因此本文主要围绕着先使用，再研究源码顺序，逐步段解析，从易到难。
二 BeanFactoryPostProcessor接口及其应用
BeanFactory 后置处理器BeanFactoryPostProcessor接口是Spring留给用户自己拓展的接口。直接debug代码，基本上都是空方法，因此debug前需要将BeanFactoryPostProcessor接口的实现添加到Spring的配置文件中。
2.1 Spring配置文件
<bean id="myBeanPostProcessor" class="com.service.MyBeanPostProcessor"/>
2.2 应用代码
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
//构造函数
public MyBeanFactoryPostProcessor() {
System.out.println("这是MyBeanFactoryPostProcessor的构造器！");
}
//回调方法
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory arg0)
throws BeansException {
System.out
.println("BeanFactoryPostProcessor调用postProcessBeanFactory方法");
}
2.3 打印日志
执行过程中会打印下面的日志
[main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'beanFactoryPostProcessor'
这是MyBeanFactoryPostProcessor的构造器！
BeanFactoryPostProcessor调用postProcessBeanFactory方法
三 源码分析
3.1 invokeBeanFactoryPostProcessors方法
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
...
}
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
...
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
//通过beanFactory获取类型为BeanFactoryPostProcessor的BeanName数组
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
//根据bean初始化的优先级分为三个list容器
//实现PriorityOrdered接口的bean优先级最高
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
//实现Ordered接口的bean优先级居中
List<String> orderedPostProcessorNames = new ArrayList<>();
//其他bean优先级居排在最后
//变量BeanName
for (String ppName : postProcessorNames) {
//判断是否被执行过的后置处理器
if (processedBeans.contains(ppName)) {
//若是，则跳过不执行任何操作
// skip - already processed in first phase above
}
//判断是否实现PriorityOrdered接口
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
//若是，获取该bean并添加到priorityOrderedPostProcessors中
//getBean的动作会检查当前 bean对象是否被实例化，如无则会触发bean的实例化，调用构造函数
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
//判断是否实现Ordered接口
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
//若是，添加到orderedPostProcessorNames中
orderedPostProcessorNames.add(ppName);
}
else {
//添加到nonOrderedPostProcessorNames中
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
//排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 调用BeanFactoryPostProcessor实现类的postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
//同理PriorityOrdered接口的实现类
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
//同理PriorityOrdered接口的实现类
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...
//在mergedBeanDefinitions中，将已经实例化的后置处理器实现类对应的bean的state设为false
//清除元数据信息，包括 allBeanNamesByType，singletonBeanNamesByType等
// 这是因为后处理器可能已经修改了原始元数据，像替换值中的占位符...
beanFactory.clearMetadataCache();
}
3.2 invokeBeanFactoryPostProcessors方法
private static void invokeBeanFactoryPostProcessors(
Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {
for (BeanFactoryPostProcessor postProcessor : postProcessors) {
//调用BeanFactoryPostProcessor实现类的postProcessBeanFactory方法
postProcessor.postProcessBeanFactory(beanFactory);
}
}
3.3 getBeanFactoryPostProcessors方法
/**
* Return the list of BeanFactoryPostProcessors that will get applied
* to the internal BeanFactory.
*/
public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {
//获取已经注册的BeanFactoryPostProcessor列表，在默认情况下返回值为空
return this.beanFactoryPostProcessors;
}
四 BeanDefinitionRegistryPostProcessor接口及其应用
BeanDefinitionRegistryPostProcessor接口是BeanFactoryPostProcessor接口的子接口，但是对Bean的优先级而言，实现BeanDefinitionRegistryPostProcessor接口的Bean对象的优先级高于实现BeanFactoryPostProcessor接口的Bean对象。
4.1 Spring配置文件
<bean id="myBeanDefinitionRegistryPostProcessor" class="com.service.MyBeanDefinitionRegistryPostProcessor"/>
4.2 应用代码
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
public MyBeanDefinitionRegistryPostProcessor() {
System.out.println("这是MyBeanDefinitionRegistryPostProcessor的构造器！");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("MyBeanDefinitionRegistryPostProcessor调用postProcessBeanDefinitionRegistry方法");
}
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("MyBeanDefinitionRegistryPostProcessor调用postProcessBeanFactory方法");
}
}
4.3 打印日志
执行过程中会打印下面的日志
这是MyBeanDefinitionRegistryPostProcessor的构造器！
MyBeanDefinitionRegistryPostProcessor调用postProcessBeanDefinitionRegistry方法
MyBeanDefinitionRegistryPostProcessor调用postProcessBeanFactory方法
五 源码分析2
invokeBeanFactoryPostProcessors源码很长，但是很多都是重复的。只要抓住主线，即Bean实例化过程的优先级：实现PriorityOrdered接口的Bean > 实现Ordered接口的Bean > 两者都没用实现的Bean，就可以轻松读懂！
5.1 invokeBeanFactoryPostProcessors
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
//存储已经处理过的BeanDefinitionRegistryPostProcessors类型的Bean
Set<String> processedBeans = new HashSet<>();
//ConfigurableListableBeanFactory是BeanDefinitionRegistry接口的实现类，因此是其实例
if (beanFactory instanceof BeanDefinitionRegistry) {
//向上转型
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
//封装两个list容器，将beanFactoryPostProcessors中存储的BeanFactoryPostProcessor对象添加到regularPostProcessors容器，另外一个存储到registryProcessors容器中
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
//上面的源码分析提到过，beanFactoryPostProcessors对象的容量默认为空，因此不会执行fo循环内容
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
//判断beanFactoryPostProcessors存储的对象是否属于BeanDefinitionRegistryPostProcessor，将对象分别存储到两个不同容器中
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
//调用BeanDefinitionRegistryPostProcessor实现类的postProcessBeanDefinitionRegistry方法
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
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.
//下面这段代码主要用于实现PriorityOrdered接口的实现类，这类Bean的优先级最高
//这里的current是指当前ben工厂beanFactory
//定义一个BeanDefinitionRegistryPostProcessor类型的集合容器，用于存储beanFactory中实例为BeanDefinitionRegistryPostProcessor的Bean
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
//获取类型为BeanDefinitionRegistryPostProcessor的BeanName数组
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
//遍历包含BeanName数组
for (String ppName : postProcessorNames) {
//判断是否实现PriorityOrdered接口
//实现PriorityOrdered接口的Bean实例化顺序的优先级更高
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
//若是，则放入currentRegistryProcessors中
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
//排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
//添加到registryProcessors中
registryProcessors.addAll(currentRegistryProcessors);
//调用实现类的postProcessBeanDefinitionRegistry方法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
//清空currentRegistryProcessors容器
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
// 这段代码通上面的类似，主要用于实现Ordered接口的实现类，这类Bean的优先级中等
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
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();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 这段代码通上面的类似，主要用于没用实现PriorityOrdered和Ordered接口的实现类，这类Bean的优先级最低
//是否重试
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();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
//回调registryProcessors和regularPostProcessors中存储Bean对象的postProcessBeanFactory方法
postProcessBeanFactory
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
...
}
六 参考文献
1）JDK7在线文档
https://tool.oschina.net/apidocs/apidoc?api=jdk_7u4
2) JDK8在线文档
https://docs.oracle.com/javase/8/docs/api/
3) Bruce Eckel. Java编程思想，第4版，2007，机械工业出版社
4）方腾飞，魏鹏，程晓明. Java并发编程的艺术，第1版，2015年，机械工业出版社
5）克雷格.沃斯. Spring实战，第5版，2020年，人民邮电出版社