Spring后处理器-BeanPostProcessor

• Bean被实例化后，到最终缓存到名为singletonObjects单例池之前，中间会经过bean的初始化过程（（该后处理器的执行时机）），例如：属性的填充、初始化方法init的执行等，其中有一个对外拓展的点BeanPostProcessor，我们称之为bean后处理器。与上文bean工厂后处理器相似，它也是一个接口，实现了该接口并被容器管理的BeanPostProcessor（即在配置文件中对其进行配置），会在流程节点上被Spring自动调用。
• BeanPostProcessor接口代码如下

  • //
    // Source code recreated from a .class file by IntelliJ IDEA
    // (powered by FernFlower decompiler)
    //
    
    package org.springframework.beans.factory.config;
    
    import org.springframework.beans.BeansException;
    import org.springframework.lang.Nullable;
    
    public interface BeanPostProcessor {
        @Nullable
        default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
            return bean;
        }
    
        @Nullable
        default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            return bean;
        }
    }
    

• 创建实现该接口（BeanPsotProcessor）的类，要在配置文件中进行管理
  • 快捷键 ctrl + insert 重写接口方法

  • package com.example.PostProcessor;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    
    public class MyBeanPostProcessor implements BeanPostProcessor {
        @Override
        public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
            System.out.println(beanName + ":postProcessBeforeInitialization");
            return bean;
        }
    
        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            System.out.println(beanName + ":postProcessAfterInitialization");
            return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
        }
    }
    

• 测试类代码

  • package com.example.Test;
    
    
    import com.example.Service.Impl.UserServiceImpl;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    public class TestApplicationContext {
        public static void main(String[] args) {
            ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
            System.out.println(context.getBean(UserServiceImpl.class));
        }
    }
    

• 运行结果如下

  • 
     

  • 展示了该后处理器的执行时机 

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Before和After执行时机

• 在Bean实例化过程可以配置相关对于bean对象的操作方法，具体间往期文章：Bean的配置- CSDN搜索
• 注册为bean的类

  • package com.example.Service.Impl;
    
    import com.example.DAO.UserDAO;
    import com.example.Service.UserService;
    import org.springframework.beans.factory.InitializingBean;
    
    import java.util.List;
    import java.util.Map;
    import java.util.Set;
    
    
    public class UserServiceImpl implements UserService, InitializingBean {
        // todo 无参构造方法
        public UserServiceImpl() {
            System.out.println("UserServiceImpl实例化");
        }
    
        // todo 自定义初始化方法
        public void init() {
            System.out.println("自定义初始化方法init()");
        }
    
        @Override
        public void afterPropertiesSet() throws Exception {
            System.out.println("属性设置之后执行afterPropertiesSet()");
        }
    
    }
    

• 实现bean后处理器的类

  • package com.example.PostProcessor;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    
    public class MyBeanPostProcessor implements BeanPostProcessor {
        @Override
        public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
            System.out.println(beanName + ":postProcessBeforeInitialization");
            return bean;
        }
    
        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            System.out.println(beanName + ":postProcessAfterInitialization");
            return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
        }
    }
    

• 配置文件

  • <?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
           xmlns:context="http://www.springframework.org/schema/context"
           xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
        <bean class="com.example.PostProcessor.MyBeanPostProcessor"></bean>
        <bean id="userService" class="com.example.Service.Impl.UserServiceImpl" init-method="init">
    </beans>

• 测试类

  • package com.example.Test;
    
    
    import com.example.Service.Impl.UserServiceImpl;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    public class TestApplicationContext {
        public static void main(String[] args) {
            ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
            System.out.println(context.getBean(UserServiceImpl.class));
        }
    }
    

• 运行结果

  • 

小结 

• 从上述运行结果来看，首先完成bean对象的创建，然后执行后处理器中的before方法，然后执行属性设置之后的方法，然后执行自定义的初始化方法，最后执行后处理器的after方法

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案例

• 对Bean方法进行执行时间日志增强
• 要求
  • Bean的方法执行之前控制台打印当前时间
  • Bean的方法执行之后控制台打印当前时间
• 分析
  • 对方法进行增强主要就是代理设计模式和包装设计模式
  • 由于Bean方法不确定，所以使用动态代理在运行期间执行增强操作
  • 在Bean实例创建完毕之后，进入到单例之前，使用Proxy真实的目标bean