spring的bean周期中BeanPostProcessor浅析-蒲公英云

参考：https://www.cnblogs.com/sishang/p/6576665.html

　　　https://www.jianshu.com/p/890446a3d477

1. 基本概念

spring容器在实例化bean之后（通过构造器创建对象并注入属性值即为实例化），可以使用BeanPostProcessor接口在bean的初始化方法前后根据需要做自己的逻辑处理。

2. BeanPostProcessor后置处理器的使用

BeanPostProcessor接口有两个方法，postProcessBeforeInitialization和postProcessAfterInitialization，默认情况下后置处理器会处理容器中所有的bean。

postProcessBeforeInitialization在bean初始化方法之前调用，初始化方法包括：bean标签添加init-method属性指定Java类中初始化方法、 @PostConstruct注解指定初始化方法，Java类实现InitailztingBean接口所产生的afterPropertiesSet()方法等。

postProcessAfterInitialization在bean初始化方法之后调用。

public class PostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException {
        if ("narCodeService".equals(beanName)) {//此方法获取容器中所有的bean，根据 beanName 名称选择要处理的bean，此处过滤实例ID为narCodeService
            return bean;
        }
        System.out.println("后置处理器处理bean=【"+beanName+"】开始");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean,
            String beanName) throws BeansException {
        if ("narCodeService".equals(beanName)) {
            return bean;
        }
        System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }
}

上段代码两个方法的第一个参数为bean对象，第二个参数为bean对象的全称名称（包名加类名）。然后该实现类配置在spring配置文件中就可以使用了。多个后置处理器按照配置顺序执行，可以配置order属性进行设置优先级。

然后将PostProcessor注入到spring容器中，比如配置到application.xml文件中。

下面有个完成实例：

package renchaofeng;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class PostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if("messageService".equals(beanName)) {
            System.out.println("messageService init method after..");
        }
        if("testnreImpl".equals(beanName)) {
            System.out.println("testnreImpl init method after..");
        }
        return bean;
    }
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if("messageService".equals(beanName)) {
            System.out.println("messageService init method before..");
        }
        if("testnreImpl".equals(beanName)) {
            System.out.println("testnreImpl init method before..");
        }
        return bean;
    }
}

将 PostProcessor配置到spring容器中，

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd" default-autowire="byName">
    <bean id="postProcessor" class="renchaofeng.PostProcessor"/>
</beans>

分别定义两个接口和其实现类：

package renchaofeng;
public interface MessageService {
    String getMessage();
}
package renchaofeng;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class MessageServiceImpl implements MessageService,InitializingBean {
    public String getMessage() {
        return "hello world";
    }
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("message init method...");
    }
}
package renchaofeng;
public interface Testnre {
 void getRen();
}
package renchaofeng;
import org.springframework.beans.factory.InitializingBean;
public class TestnreImpl implements Testnre,InitializingBean {
    @Override
    public void getRen() {
         System.out.println("fffff..");
    }
    @Override
    public void afterPropertiesSet() throws Exception {
         System.out.println("TestnreImpl init method..");
    }
}

然后把上面两个实现类配置到spring容器中：

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd" default-autowire="byName">
    <bean id="messageService" class="renchaofeng.MessageServiceImpl"/>
    <bean id="postProcessor" class="renchaofeng.PostProcessor"/>
    <bean id="testnreImpl" class="renchaofeng.TestnreImpl"/>
</beans>

写个测试类如下：

package renchaofeng;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestSpring {
    public static void main(String[] args) throws BeansException{ 
         ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring/application-ren.xml");
         System.out.println("context 启动成功");
         MessageService messageService = (MessageService)context.getBean("messageService");
         System.out.println(messageService.getMessage());
    }
}

运行结果如下：

messageService init method before..
message init method…
messageService init method after..
testnreImpl init method before..
TestnreImpl init method..
testnreImpl init method after..
context 启动成功
hello world

说明每当一个bean执行初始化方法时，都会调用BeanPostProcessor的postProcessBeforeInitialization和postProcessAfterInitialization方法。