文章目录

• Pre
• org.springframework.beans.factory.config.BeanFactoryPostProcessor
• 源码探究
• • 1 是否实现BeanDefinitionRegistryPostProcessor 接口，分别写入集合
  • 2 处理实现了的PriorityOrdered和 BeanDefinitionRegistryPostProcessors 的 bean
  • 3. 处理实现了的Ordered和BeanDefinitionRegistryPostProcessors 的 bean
  • 4 处理其他实现了BeanDefinitionRegistryPostProcessor的bean
  • 5 invokeBeanFactoryPostProcessors
  • 6 除了试下BeanDefinitionRegistryPostProcessor之外的其他 实现了BeanFactoryPostProcessor接口的bean 分类
  • 7 处理 PriorityOrdered ，invokeBeanDefinitionRegistryPostProcessors
  • 8 处理 Ordered ，invokeBeanDefinitionRegistryPostProcessors
  • 9 处理剩下的 ，invokeBeanDefinitionRegistryPostProcessors
  • 10 invokeBeanDefinitionRegistryPostProcessors & invokeBeanFactoryPostProcessors 分析
• BeanFactoryPostProcessor的处理流程
• 扩展方式

Pre

Spring Boot - 扩展接口一览

org.springframework.beans.factory.config.BeanFactoryPostProcessor

这个接口是beanFactory的扩展接口，调用时机在spring在读取beanDefinition信息之后，实例化bean之前。

在这个时机，用户可以通过实现这个扩展接口来自行处理一些东西，比如修改已经注册的beanDefinition的元信息

package org.springframework.beans.factory.config;import org.springframework.beans.BeansException;/*** Factory hook that allows for custom modification of an application context's* bean definitions, adapting the bean property values of the context's underlying* bean factory.** 
Useful for custom config files targeted at system administrators that* override bean properties configured in the application context. See* {@link PropertyResourceConfigurer} and its concrete implementations for* out-of-the-box solutions that address such configuration needs.** 
A {@code BeanFactoryPostProcessor} may interact with and modify bean* definitions, but never bean instances. Doing so may cause premature bean* instantiation, violating the container and causing unintended side-effects.* If bean instance interaction is required, consider implementing* {@link BeanPostProcessor} instead.** 
Registration
* 
An {@code ApplicationContext} auto-detects {@code BeanFactoryPostProcessor}* beans in its bean definitions and applies them before any other beans get created.* A {@code BeanFactoryPostProcessor} may also be registered programmatically* with a {@code ConfigurableApplicationContext}.** 
Ordering
* 
{@code BeanFactoryPostProcessor} beans that are autodetected in an* {@code ApplicationContext} will be ordered according to* {@link org.springframework.core.PriorityOrdered} and* {@link org.springframework.core.Ordered} semantics. In contrast,* {@code BeanFactoryPostProcessor} beans that are registered programmatically* with a {@code ConfigurableApplicationContext} will be applied in the order of* registration; any ordering semantics expressed through implementing the* {@code PriorityOrdered} or {@code Ordered} interface will be ignored for* programmatically registered post-processors. Furthermore, the* {@link org.springframework.core.annotation.Order @Order} annotation is not* taken into account for {@code BeanFactoryPostProcessor} beans.** @author Juergen Hoeller* @author Sam Brannen* @since 06.07.2003* @see BeanPostProcessor* @see PropertyResourceConfigurer*/
@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;}

spring容器初始化时，从资源中读取到bean的相关定义后，保存在beanFactory的成员变量中（DefaultListableBeanFactory#beanDefinitionMap）

private final Map beanDefinitionMap = new ConcurrentHashMap<>(256);

实例化bean的操作就是依据这些BeanDefinition来做的。

在实例化之前，spring允许我们通过自定义扩展来改变bean的定义，定义一旦变了，后面的实例也就变了，而beanFactory后置处理器BeanFactoryPostProcessor就是用来改变bean定义的。

源码探究

AbstractApplicationContext#refresh 继续走起

继续

// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

主要功能是： 找出所有beanFactory后置处理器，并且调用这些处理器来改变bean的定义

继续 org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors

	/*** Instantiate and invoke all registered BeanFactoryPostProcessor beans,* respecting explicit order if given.* 
Must be called before singleton instantiation.*/protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());.......

我们重点关注PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

代码比较长，我们逐段看一下

1 是否实现BeanDefinitionRegistryPostProcessor 接口，分别写入集合

	for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {BeanDefinitionRegistryPostProcessor registryProcessor =(BeanDefinitionRegistryPostProcessor) postProcessor;registryProcessor.postProcessBeanDefinitionRegistry(registry);registryProcessors.add(registryProcessor);}else {regularPostProcessors.add(postProcessor);}}

遍历入参 beanFactoryPostProcessors ， 是否实现了BeanDefinitionRegistryPostProcessor，分别放入两个集合：registryProcessors和regularPostProcessors；

2 处理实现了的PriorityOrdered和 BeanDefinitionRegistryPostProcessors 的 bean

// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.String[] postProcessorNames =beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);for (String ppName : postProcessorNames) {if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));processedBeans.add(ppName);}}sortPostProcessors(currentRegistryProcessors, beanFactory);registryProcessors.addAll(currentRegistryProcessors);invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());currentRegistryProcessors.clear();

找出所有实现了BeanDefinitionRegistryPostProcessor接口和PriorityOrdered接口的bean，放入registryProcessors集合，根据PriorityOrdered接口来排序，然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行；

3. 处理实现了的Ordered和BeanDefinitionRegistryPostProcessors 的 bean

// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.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, beanFactory.getApplicationStartup());currentRegistryProcessors.clear();

找出所有实现了BeanDefinitionRegistryPostProcessor接口和Ordered接口的bean，放入registryProcessors集合，根据Ordered接口来排序，然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行；

4 处理其他实现了BeanDefinitionRegistryPostProcessor的bean

	// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.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, beanFactory.getApplicationStartup());currentRegistryProcessors.clear();}

对于那些实现了BeanDefinitionRegistryPostProcessor接口，但是没有实现PriorityOrdered和Ordered的bean也被找出来，然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行

5 invokeBeanFactoryPostProcessors

// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);

6 除了试下BeanDefinitionRegistryPostProcessor之外的其他 实现了BeanFactoryPostProcessor接口的bean 分类

	// Do not initialize FactoryBeans here: We need to leave all regular beans// uninitialized to let the bean factory post-processors apply to them!String[] postProcessorNames =beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,// Ordered, and the rest.List priorityOrderedPostProcessors = new ArrayList<>();List orderedPostProcessorNames = new ArrayList<>();List nonOrderedPostProcessorNames = new ArrayList<>();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);}}

找出实现了BeanFactoryPostProcessor接口的bean，注意这里已将前面实现了BeanDefinitionRegistryPostProcessor接口的bean给剔除了

if (processedBeans.contains(ppName)) {// skip - already processed in first phase above
}

将这些bean分为三类：

• 实现了PriorityOrdered接口的放入priorityOrderedPostProcessors，
• 实现了Ordered接口的放入orderedPostProcessorNames，
• 其他的放入nonOrderedPostProcessorNames，这段代码是关键，自定义的实现BeanFactoryPostProcessor接口的bean就会在此处被查找出来。

7 处理 PriorityOrdered ，invokeBeanDefinitionRegistryPostProcessors

// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.sortPostProcessors(priorityOrderedPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

8 处理 Ordered ，invokeBeanDefinitionRegistryPostProcessors

// Next, invoke the BeanFactoryPostProcessors that implement Ordered.List orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());for (String postProcessorName : orderedPostProcessorNames) {orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}sortPostProcessors(orderedPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

9 处理剩下的 ，invokeBeanDefinitionRegistryPostProcessors

// Finally, invoke all other BeanFactoryPostProcessors.List nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());for (String postProcessorName : nonOrderedPostProcessorNames) {nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

10 invokeBeanDefinitionRegistryPostProcessors & invokeBeanFactoryPostProcessors 分析

从上面的分析可以发现，所有实现了BeanFactoryPostProcessor接口的bean，都被作为入参，然后调用了invokeBeanDefinitionRegistryPostProcessors或者invokeBeanFactoryPostProcessors方法去处理

	/*** Invoke the given BeanDefinitionRegistryPostProcessor beans.*/private static void invokeBeanDefinitionRegistryPostProcessors(Collection postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process").tag("postProcessor", postProcessor::toString);postProcessor.postProcessBeanDefinitionRegistry(registry);postProcessBeanDefRegistry.end();}}

	/*** Invoke the given BeanFactoryPostProcessor beans.*/private static void invokeBeanFactoryPostProcessors(Collection postProcessors, ConfigurableListableBeanFactory beanFactory) {for (BeanFactoryPostProcessor postProcessor : postProcessors) {StartupStep postProcessBeanFactory = beanFactory.getApplicationStartup().start("spring.context.bean-factory.post-process").tag("postProcessor", postProcessor::toString);postProcessor.postProcessBeanFactory(beanFactory);postProcessBeanFactory.end();}}

对每个BeanFactoryPostProcessor接口的实现类，都调用了其接口方法。
不同的是 对于实现了BeanDefinitionRegistryPostProcessor接口的bean，调用其postProcessBeanDefinitionRegistry方法的时候，入参是BeanDefinitionRegistry，而非BeanFactory，因此，实现了BeanDefinitionRegistryPostProcessor接口的bean，其postProcessBeanDefinitionRegistry在被调用时，可以通过入参BeanDefinitionRegistry来做更多和bean的定义有关的操作，例如注册bean等等、

BeanFactoryPostProcessor的处理流程

小结一下：

• ApplicationContext扩展类可以调用AbstractApplicationContext.addBeanFactoryPostProcessor方法，将自定义的BeanFactoryPostProcessor实现类保存到ApplicationContext中；
• spring容器初始化时，上一步中被加入到ApplicationContext的bean会被优先调用其postProcessBeanFactory方法；
• 自定义的BeanFactoryPostProcessor接口实现类，也会被找出来，然后调用其postProcessBeanFactory方法；
• postProcessBeanFactory方法被调用时，beanFactory会被作为参数传入，自定义类中可以使用该参数来处理bean的定义，达到业务需求；
• 此时的spring容器还没有开始实例化bean，因此自定义的BeanFactoryPostProcessor实现类不要做与bean实例有关的操作，而是做一些与bean定义有关的操作，例如修改某些字段的值，这样后面实例化的bean的就会有相应的改变；

扩展方式

package com.artisan.bootspringextend.testextends;import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.context.annotation.Configuration;/*** @author 小工匠* @version 1.0 * @date 2022/11/27 16:58* @mark: show me the code , change the world*/@Slf4j
@Configuration
public class ExtendBeanFactoryPostProcessor implements BeanFactoryPostProcessor {@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {log.info("----->postProcessBeanFactory called ");}
}