Spring Bean的生命周期详解

（1）Spring Bean的生命周期介绍

Bean的生命周期简单分为4个阶段：实例化、属性赋值、初始化和销毁。实例化和属性赋值对应构造方法和setter方法的注入。

Spring之所以强大的原因是易扩展，生命周期相关的常用扩展点非常多。扩展点分2类：

1. 作用于多个Bean的增强扩展

InstantiationAwareBeanPostProcessor 作用于实例化阶段前后

BeanPostProcessor 作用于初始化阶段前后

2. 作用于单个bean的增强扩展

初始化阶段：Aware接口（BeanNameAware BeanClassLoaderAware BeanFactoryAware）

（2）Spring Bean的生命周期流程图

（3）代码演示

自定义一个InstantiationAwareBeanPostProcessor

package com.learn.blog.demo;
 
import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
 
public class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {
    /**
     * 在目标对象实例化之前调用，该方法的返回值类型是Object，我们可以返回任何类型的值。
     * 由于这个时候目标对象还未实例化，所以这个返回值可以用来代替原本该生成的目标对象的实例(比如代理对象)。
     * 如果该方法的返回值代替原本该生成的目标对象，后续只有postProcessAfterInitialization方法会调用，其它方法不再调用；否则按照正常的流程走
     */
    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        if ("demo6".equals(beanName)) {
            System.out.println("执行InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation方法");
        }
        return InstantiationAwareBeanPostProcessor.super.postProcessBeforeInstantiation(beanClass, beanName);
    }
 
    /**
     * 在目标对象实例化之后调用，但是该实例的属性还未被设置。
     * 它的返回值决定要不要调用postProcessProperties方法的其中一个因素（另一个因素是mbd.getDependencyCheck()）；
     * 如果该方法返回false,并且不需要check，那么postProcessProperties就会被忽略不执行；
     * 如果返回true，postProcessProperties就会被执行
     */
    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        if ("demo6".equals(beanName)) {
            System.out.println("执行InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation方法");
        }
        return InstantiationAwareBeanPostProcessor.super.postProcessAfterInstantiation(bean, beanName);
    }
 
    /**
     * 对属性值进行修改，这个时候属性值还未赋值给目标对象
     */
    @Override
    public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
        if ("demo6".equals(beanName)) {
            System.out.println("执行InstantiationAwareBeanPostProcessor的postProcessProperties方法");
        }
        return InstantiationAwareBeanPostProcessor.super.postProcessProperties(pvs, bean, beanName);
    }
}

自定义一个BeanPostProcessor

package com.learn.blog.demo;
 
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
 
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if ("demo6".equals(beanName)) {
            System.out.println("执行BeanPostProcessor的postProcessBeforeInitialization方法");
        }
        return BeanPostProcessor.super.postProcessBeforeInitialization(bean, beanName);
    }
 
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if ("demo6".equals(beanName)) {
            System.out.println("执行BeanPostProcessor的postProcessAfterInitialization方法");
        }
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
}

自定义一个bean

package com.learn.blog.demo;
 
 
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.BeanNameAware;
 
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
 
// 实现BeanNameAware, BeanFactoryAware接口
public class Demo6 implements BeanNameAware, BeanFactoryAware {
    private String name;
 
    public Demo6() {
        System.out.println("执行构造函数实例化");
    }
 
    // 重写BeanNameAware的方法
    @Override
    public void setBeanName(String s) {
        System.out.println("执行BeanNameAware的setBeanName方法");
    }
 
    // 重写BeanFactoryAware的方法
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("执行BeanFactoryAware的setBeanFactory方法");
    }
 
    // init-method
    private void init() {
        System.out.println("初始化方法");
    }
 
    // destory-method
    private void destroy() {
        System.out.println("销毁方法");
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        System.out.println("注入属性name");
        this.name = name;
    }
}

spring的配置文件BeanLifecycle.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 id="demo6" class="com.learn.blog.demo.Demo6"
          init-method="init" destroy-method="destroy">
        <property name="name" value="文大奇Quiin"></property>
    </bean>
 
    <bean id="myBeanPostProcessor" class="com.learn.blog.demo.MyBeanPostProcessor">
 
    </bean>
 
    <bean id="myInstantiationAwareBeanPostProcessor" class="com.learn.blog.demo.MyInstantiationAwareBeanPostProcessor">
    </bean>
 
</beans>

启动类

public class BlogDemoApplication {
 
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("BeanLifecycle.xml");
        applicationContext.getBean("demo6");
        ((ClassPathXmlApplicationContext) applicationContext).close();
    }
 
}

执行结果

执行InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation方法
执行构造函数实例化
执行InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation方法
执行InstantiationAwareBeanPostProcessor的postProcessProperties方法
注入属性name
执行BeanNameAware的setBeanName方法
执行BeanFactoryAware的setBeanFactory方法
执行BeanPostProcessor的postProcessBeforeInitialization方法
初始化方法
执行BeanPostProcessor的postProcessAfterInitialization方法
销毁方法