Spring Bean的生命周期

Posted 2020-09-06 昵称001

在传统的java应用中，bean的生命周期由new进行bean的实例化，然后该bean就可以使用了，当bean不被使用时，由java自动进行垃圾回收。

然而Spring的生命周期相对比较复杂：

1.Spring对bean进行实例化，即调用构造器

public MyBean01(){
        System.out.println("MyBean01 构造");
    }

 

2.Spring将值和bean的引用注入到bean对应的属性中，即调用set~方法

public void setName(String name) {
        System.out.println("MyBean01  值注入属性中");
        this.name = name;
    }

 

3.如果该bean实现了BeanNameAware接口，Spring将bean的id传递给setBeanName()方法

@Override
    public void setBeanName(String name) {
        System.out.println("MyBean01 id: "+name);
    }

4.如果该bean实现了BeanFactoryAware接口，Spring将调用setBeanFactory()方法，将BeanFactory实例传入

@Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("BeanFactory 中有 b1 这个bean： "+beanFactory.containsBean("b1"));
        System.out.println("BeanFactory 调用MyBean02.class："+beanFactory.getBean(MyBean02.class).toString());
    }

5.如果该bean实现了ApplicationContextAware接口，Spring将调用setApplicationContext()方法，将bean所在的应用上下文的引用传入

@Override
    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException {
        applicationContext.isSingleton(name);
    }

6.如果bean实现了BeanPostProcessor接口，Spring将调用它的postProcessBeforeInitialization方法

@Override
    public Object postProcessBeforeInitialization(Object bean, String beanName)
            throws BeansException {
        
        //在这里可以修改bean的属性，返回时得返回bean，不然程序不予执行
        return bean;
    }

7.如果bean实现了InitializingBean接口，Spring将调用它的afterPropertiesSet()方法，另一种方法是在xml文件中配置init-method

<bean id="b1" class="com.spring.cycle.MyBean01" 
        init-method="init" 
　　　　 destroy-method="distory"> 
        <property name="name" value="tom"></property>
</bean>

8.如果bean实现了BeanPostProcessor接口，Spring将调用它的postProcessAfterInitialization，与步骤6协同操作卡住步骤7(init)

@Override
    public Object postProcessAfterInitialization(Object bean, String beanName)
            throws BeansException {
        // TODO Auto-generated method stub
        return null;
    }

9.此时，bean已经准备就绪，一直存在应用上下文中，直到该应用上下文被销毁

10.当应用上下文关闭时，如果bean实现了DisposableBean接口，Spring将调用它的destory()方法，或者在xml文件中配置destory-method

 

以下是4段代码，以供测试

package com.spring.cycle;

import org.springframework.beans.factory.BeanNameAware;


public class MyBean01 implements BeanNameAware{
    
    public MyBean01(){
        System.out.println("MyBean01 构造");
    }
    @Override
    protected void finalize() throws Throwable {
        System.out.println("MyBean01 finalize");
        super.finalize();
    }
    public void init(){
        System.out.println("MyBean01 init");
    }
    public void distory(){
        System.out.println("MyBean01 distory");
    }
    
    private String name;
    
    public void setName(String name) {
        System.out.println("MyBean01  值注入属性中");
        this.name = name;
    }
    
    @Override
    public String toString() {
        return "MyBean01: name--> "+name;
    }
    @Override
    public void setBeanName(String name) {
        System.out.println("MyBean01 id: "+name);
    }

}

package com.spring.cycle;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class MyBean02 implements BeanFactoryAware,ApplicationContextAware,BeanPostProcessor{
    
    public MyBean02(){
        System.out.println("MyBean02 构造");
    }
    @Override
    protected void finalize() throws Throwable {
        System.out.println("MyBean02 finalize");
        super.finalize();
    }
    private void init(){
        System.out.println("MyBean02 init");
    }
    private void distory(){
        System.out.println("MyBean02 distory");
    }
    
    private String name;
    public void setName(String name) {
        System.out.println("MyBean02  值注入属性中");
        this.name = name;
    }
    
    @Override
    public String toString() {
        return "MyBean02: name--> "+name;
    }
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("MyBean02 BeanFactory 中有 b1 这个bean： "+beanFactory.containsBean("b1"));
        System.out.println("MyBean02 BeanFactory 调用MyBean02.class："+beanFactory.getBean(MyBean02.class).toString());
    }
    @Override
    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException {
        //applicationContext.isSingleton(name);
        System.out.println("MyBean02 applicationContext.......");
    }
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName)
            throws BeansException {
        
        //在这里可以修改bean的属性，返回时得返回bean，不然程序不予执行
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName)
            throws BeansException {
        // TODO Auto-generated method stub
        return null;
    }

}

<?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 id="b1" class="com.spring.cycle.MyBean01" 
        init-method="init" destroy-method="distory"> 
        <property name="name" value="tom"></property>
    </bean>
    <bean id="b2" class="com.spring.cycle.MyBean02" 
        init-method="init" destroy-method="distory"> 
        <property name="name" value="jerry"></property>    
    </bean>

</beans>

package com.spring.cycle;

import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestMain {
    public static void main(String[] args) {
        
        ConfigurableApplicationContext context = new ClassPathXmlApplicationContext("com/spring/cycle/bean-cycle.xml");
        
        MyBean01  b1 = (MyBean01) context.getBean("b1");
        MyBean02  b2 = (MyBean02) context.getBean("b2");
        
        System.out.println(b1);
        System.out.println(b2);
        
         
        context.close();
    }

}