概述

BeanPostProcessor：Bean对象的后置处理器，负责对已创建好的bean对象进行加工处理；

BeanPostProcessor中的两个核心方法：
postProcessBeforeInitialization：在每个bean对象的初始化方法执行之前执行该方法，如InitializingBean的afterPropertiesSet方法；
postProcessAfterInitialization：在每个bean对象的初始化方法执行之后执行该方法，如InitializingBean的afterPropertiesSet方法；

基本使用

项目结构

项目代码

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com</groupId><artifactId>spring-bean-post-processor</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target></properties><dependencies><dependency><groupId>org.springframework</groupId><artifactId>spring-core</artifactId><version>5.2.1.RELEASE</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-beans</artifactId><version>5.2.1.RELEASE</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>5.2.1.RELEASE</version></dependency></dependencies></project>

AutowireBean.java

package com.spring.bean;import org.springframework.stereotype.Component;/*** @author honey* @date 2023-08-11 16:50:19*/
@Component
public class AutowireBean {public void autowire(){System.out.println("AutowireBean 执行autowire()");}}

UserBean.java

package com.spring.bean;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;/*** @author honey* @date 2023-08-11 16:48:33*/
@Component
public class UserBean {private AutowireBean autowireBean;public UserBean() {System.out.println("UserBean 执行构造方法");}@Autowiredpublic void setAutowireBean(AutowireBean autowireBean) {System.out.println("UserBean 依赖注入：" + autowireBean);this.autowireBean = autowireBean;}@PostConstructpublic void init() {System.out.println("UserBean 执行init()");}@PreDestroypublic void destroy() {System.out.println("UserBean 执行destroy()");}public void autowire() {System.out.println("UserBean 执行autowire()");autowireBean.autowire();}
}

MyBeanPostProcessor.java

package com.spring.processor;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;/*** @author honey* @date 2023-08-11 16:42:27*/
@Component
public class MyBeanPostProcessor implements BeanPostProcessor {private final String beanName = "userBean";/*** 在每个bean对象的初始化方法执行之前执行** @param bean     bean对象* @param beanName bean名称* @return 在调用init初始化之前，可以修改原有bean对象，如果返回为null，则直接返回原有bean对象* @throws BeansException BeansException*/@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (this.beanName.equals(beanName)) {System.out.println("UserBean 执行postProcessBeforeInitialization方法");System.out.println("UserBean 实例对象：" + bean);}return bean;}/*** 在每个bean对象的初始化方法执行之后执行** @param bean     bean对象* @param beanName bean名称* @return 在调用init初始化之后，可以修改原有bean对象，如果返回为null，则直接返回原有bean对象* @throws BeansException BeansException*/@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {if (this.beanName.equals(beanName)) {System.out.println("UserBean 执行postProcessAfterInitialization方法");System.out.println("UserBean 实例对象：" + bean);}return bean;}
}

SpringConfig.java

package com.spring.config;import org.springframework.context.annotation.ComponentScan;/*** @author honey* @date 2023-08-11 16:51:26*/
@ComponentScan(value = {"com.spring.bean,com.spring.processor"})
public class SpringConfig {}

SpringTest01.java

package com.spring.test;import com.spring.bean.UserBean;
import com.spring.config.SpringConfig;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;/*** @author honey* @date 2023-08-11 16:53:30*/
public class SpringTest01 {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);UserBean userBean = applicationContext.getBean("userBean", UserBean.class);System.out.println("--------------------------");System.out.println("UserBean 实例对象：" + userBean);userBean.autowire();System.out.println("--------------------------");applicationContext.close();}
}

运行结果

从运行结果可以看到，postProcessBeforeInitialization方法在init()方法执行之前执行，而postProcessAfterInitialization方法在init()方法执行之后执行。

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在postProcessBeforeInitialization和postProcessAfterInitialization方法中可以对原有的bean对象进行修改，如果方法的返回值为null，则不会对原有的bean对象进行修改。

第一种情况：返回值为原有bean对象

第二种情况：返回值为null

运行结果：

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第三种情况：返回值不是原有的bean对象

运行结果：

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源代码

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AbstractAutowireCapableBeanFactory.java

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常用处理器

AutowiredAnnotationBeanPostProcessor：处理@Autowired注解
CommonAnnotationBeanPostProcessor：处理@Resource注解

项目结构

项目代码

OrderBean.java

package com.spring.bean;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.annotation.Resource;/*** @author honey* @date 2023-08-12 19:16:27*/
@Component
public class OrderBean {private AutowireBean autowireBean;public OrderBean() {System.out.println("OrderBean 执行构造方法");}@Autowiredpublic void setAutowireBean1(AutowireBean autowireBean) {System.out.println("OrderBean @Autowired依赖注入：" + autowireBean);this.autowireBean = autowireBean;}@Resourcepublic void setAutowireBean2(AutowireBean autowireBean) {System.out.println("OrderBean @Resource依赖注入：" + autowireBean);this.autowireBean = autowireBean;}@PostConstructpublic void init() {System.out.println("OrderBean 执行init()");}@PreDestroypublic void destroy() {System.out.println("OrderBean 执行destroy()");}public void autowire() {System.out.println("OrderBean 执行autowire()");autowireBean.autowire();}}

SpringTest02.java

package com.spring.test;import com.spring.bean.AutowireBean;
import com.spring.bean.OrderBean;
import org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor;
import org.springframework.context.annotation.CommonAnnotationBeanPostProcessor;
import org.springframework.context.support.GenericApplicationContext;/*** @author honey* @date 2023-08-12 19:20:53*/
public class SpringTest02 {public static void main(String[] args) {GenericApplicationContext applicationContext = new GenericApplicationContext();// 注册bean对象applicationContext.registerBean("orderBean", OrderBean.class);applicationContext.registerBean("autowireBean", AutowireBean.class);// 处理@Autowired注解applicationContext.registerBean(AutowiredAnnotationBeanPostProcessor.class);// 处理@Resource注解applicationContext.registerBean(CommonAnnotationBeanPostProcessor.class);applicationContext.refresh();OrderBean orderBean = applicationContext.getBean("orderBean", OrderBean.class);System.out.println("--------------------------");System.out.println("AsyncBean 实例对象：" + orderBean);orderBean.autowire();System.out.println("--------------------------");applicationContext.close();}
}

执行结果