Spring后置处理器之-BeanPostProcessor

在bean初始化前后进行一些处理工作；

BeanPostProcessor【interface】：bean的后置处理器；
               方法postProcessBeforeInitialization（）:在初始化之前工作
               方法postProcessAfterInitialization（）:在初始化之后工作

---

*BeanPostProcessor原理

spring源码中的执行顺序： 

* populateBean(beanName, mbd, instanceWrapper);给bean进行属性赋值
 * initializeBean
 * {
 * applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
 * invokeInitMethods(beanName, wrappedBean, mbd);执行自定义初始化
 * applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
 *}

 * Spring底层对 BeanPostProcessor 的使用

 bean赋值，注入其他组件，@Autowired，生命周期注解功能，@Async,xxx;

---

 一、自定义后置处理器

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

/**
 * 后置处理器：初始化前后进行处理工作
 * 将后置处理器加入到容器中
 * @author lfy
 */
@Component
public class MyBeanPostProcessor implements BeanPostProcessor {

	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		// TODO Auto-generated method stub
		System.out.println("postProcessBeforeInitialization..."+beanName+"=>"+bean);
		return bean;
	}

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		// TODO Auto-generated method stub
		System.out.println("postProcessAfterInitialization..."+beanName+"=>"+bean);
		return bean;
	}

}

二、定义Bean类

1、Bean实现InitializingBean（定义初始化逻辑）， DisposableBean（定义销毁逻辑）接口

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;

@Component
public class Cat implements InitializingBean,DisposableBean {
	
	public Cat(){
		System.out.println("cat constructor...");
	}

	@Override
	public void destroy() throws Exception {
		// TODO Auto-generated method stub
		System.out.println("cat...destroy...");
	}

	@Override
	public void afterPropertiesSet() throws Exception {
		// TODO Auto-generated method stub
		System.out.println("cat...afterPropertiesSet...");
	}

}

2、 自定义init(),destory()方法，@Bean配置@Bean(initMethod="init",destroyMethod="detory")

package com.atguigu.bean;

import org.springframework.stereotype.Component;

@Component
public class Car {
	
	public Car(){
		System.out.println("car constructor...");
	}
	
	public void init(){
		System.out.println("car ... init...");
	}
	
	public void detory(){
		System.out.println("car ... detory...");
	}

}

3、 在初始化方法上面添加：@PostConstruct注解；在销毁方法上面添加： @PreDestroy注解；

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class Dog {
	
	public Dog(){
		System.out.println("dog constructor...");
	}
	
	//对象创建并赋值之后调用
	@PostConstruct
	public void init(){
		System.out.println("Dog....@PostConstruct...");
	}
	
	//容器移除对象之前
	@PreDestroy
	public void detory(){
		System.out.println("Dog....@PreDestroy...");
	}
	
}

三、配置类

@ComponentScan("com.atguigu.bean")
@Configuration
public class MainConfigOfLifeCycle {
	
	//@Scope("prototype")
	@Bean(initMethod="init",destroyMethod="detory")
	public Car car(){
		return new Car();
	}

}

四、测试

import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.atguigu.config.MainConfigOfLifeCycle;

public class IOCTest_LifeCycle {
	
	@Test
	public void test01(){
		//1、创建ioc容器
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
		System.out.println("容器创建完成...");
		
		//applicationContext.getBean("car");
		//关闭容器
		applicationContext.close();
	}

}

测试结果：

 

说明：单例模式下，在容器通过

【    方法一、通过@Bean指定init-method和destroy-method；

       方法二、通过让Bean实现InitializingBean（定义初始化逻辑）， DisposableBean（定义销毁逻辑）;

       方法三、可以使用JSR250；】

定义对象的初始化和销毁方法时，定义了Bean的后置处理器，在Bean初始化前后执行这两个方法。