Bean的生命周期——init-method和destroy-method - 通过让Bean实现InitializingBean，DisposableBean--BeanPostProcessor

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* bean的生命周期：
*     bean创建---初始化----销毁的过程
* 容器管理bean的生命周期；
* 我们可以自定义初始化和销毁方法；容器在bean进行到当前生命周期的时候来调用我们自定义的初始化和销毁方法
* 


* 构造（对象创建）
*     单实例：在容器启动的时候创建对象
*     多实例：在每次获取的时候创建对象\
* 


* BeanPostProcessor.postProcessBeforeInitialization
* 初始化：
*     对象创建完成，并赋值好，调用初始化方法。。。
* BeanPostProcessor.postProcessAfterInitialization


* 销毁：
*     单实例：容器关闭的时候
*     多实例：容器不会管理这个bean；容器不会调用销毁方法；

Car.java

package com.dym.bean;

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

}

MainConfigOfLifeCycle.class

package com.dym.config;

import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;

import com.dym.bean.Car;

@Configuration
public class MainConfigOfLifeCycle {
	
	//@Scope("prototype")
	@Bean(initMethod="init",destroyMethod="destroy")
	public Car car(){
		return new Car();
	}

}

IOCTest_LifeCycle.class

package com.dym.test;

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

import com.dym.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();
	}

}

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* 1）、指定初始化和销毁方法；
*     通过@Bean指定init-method和destroy-method；


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


* 3）、可以使用JSR250；
*     @PostConstruct：在bean创建完成并且属性赋值完成；来执行初始化方法
*     @PreDestroy：在容器销毁bean之前通知我们进行清理工作


* 4）、BeanPostProcessor【interface】：bean的后置处理器；
*     在bean初始化前后进行一些处理工作；
*     postProcessBeforeInitialization:在初始化之前工作
*     postProcessAfterInitialization:在初始化之后工作

Cat.class

package com.dym.bean.dd;

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...");
	}
}

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Dog.class

package com.dym.bean.dd;

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 implements ApplicationContextAware {

    //@Autowired
    private ApplicationContext applicationContext;

    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...");
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        // TODO Auto-generated method stub
        this.applicationContext = applicationContext;
    }
}

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MyBeanPostProcessor.class

package com.dym.bean.dd;

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
 */
@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;
	}
}

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BeanPostProcessor原理

* 遍历得到容器中所有的BeanPostProcessor；挨个执行beforeInitialization，
* 一旦返回null，跳出for循环，不会执行后面的BeanPostProcessor.postProcessorsBeforeInitialization
*
* BeanPostProcessor原理
* 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 BeanPostProcessor;

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