一步步剖析spring bean生命周期

Posted 2020-11-16 Alan_beijing

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关于spring bean的生命周期，是深入学习spring的基础，也是难点，本篇文章将采用代码+图文结论的方式来阐述spring bean的生命周期，

本篇文章将阐述清楚下图。

一项目结构及源码

1.程序目录结构

2.applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean class="com.demo.dao.UserDao" id="userDao" scope="singleton" init-method="myInit" destroy-method="myDestroy">
        <property name="userName" value="Alan_beijing"/>
    </bean>

    <bean class="com.demo.dao.MyBeanPostProcessor" id="myBeanPostProcessor"/>

</beans>

3.UserDao.java

package com.demo.dao;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.*;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.apache.log4j.Logger;

public class UserDao implements BeanNameAware, BeanFactoryAware, ApplicationContextAware, InitializingBean,
        DisposableBean{

    private String userName;
    private int count = 0;

    public String getUserName() {
        return userName;
    }

    //2.属性注入，注入属性为userName
    public void setUserName(String userName) {
        count++;
        System.out.println(count + "：注入属性userName="+userName);
        this.userName = userName;
    }

    //1.无参构造函数，实例化时调用该构造函数
    public UserDao() {
        count++;
        System.out.println(count + "：调用构造函数UserDao()");
    }

    //3.实现BeanNameAware，获取bean id
    public void setBeanName(String s) {
        count++;
        System.out.println(count + "：调用setBeanName()获取bean id,bean id=" + s);
    }

    //4.实现BeanFactoryAware,获取bean工厂
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        count++;
        System.out.println(count + "：调用setBeanFactory()获取bean工厂,beanFactory=" + beanFactory);
    }

    //5.实现ApplicationContextAware,获取bean上下文
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        count++;
        System.out.println(count + "：调用setApplicationContext()获取bean上下文,applicationContext=" + applicationContext);
    }

    //6.实现InitializingBean，获取afterPropertiesSet
    public void afterPropertiesSet() throws Exception {
        count++;
        System.out.println(count + "：调用afterPropertiesSet()");
    }

    //7.自定义初始化方法myInit()
    public void myInit() {
        count++;
        System.out.println(count + "：调用自定义myInit()");
    }

    //8.实现DisposableBean，获取destroy()
    public void destroy() throws Exception {
        count++;
        System.out.println(count + "：destroy()");
    }

    //9.自定义销毁方法myDestroy()
    public void myDestroy() {
        count++;
        System.out.println(count + "：调用自定义destroy()");
    }
}

4.MyBeanPostProcessor.java

package com.demo.dao;

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

public  class MyBeanPostProcessor implements BeanPostProcessor {
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("=====调用postProcessBeforeInitialization()=====");
        return bean;
    }

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("=====调用postProcessAfterInitialization()=====");
        return bean;
    }
}

二测试代码及测试结果

1.test.java

package com.demo.test;

import com.demo.dao.UserDao;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {

    @Test
    public void test() {
        //定义容器并初始化
        //ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        AbstractApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        applicationContext.getBean(UserDao.class);
        //只有关闭容器时，才会调用destroy方法
        applicationContext.registerShutdownHook();
    }
}