Spring Bean的生命周期详解

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）

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 {
    
    @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);
    }

    
    @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);
    }

    
    @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

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