深入源码理解SpringBean生命周期

概述

本文描述下Spring的实例化、初始化、销毁，整个SpringBean生命周期，聊一聊BeanPostProcessor的回调时机、Aware方法的回调时机、初始化方法的回调及其顺序、销毁方法的回调及其顺序、重要的BeanPostProcessor的介绍。
开头是一张我画的调用流转图，然后就是我写的一个Demo通过日志打印了SpringBean的生命周期，最后通过源码慢慢跟进其生命周期。

生命周期流转图

生命周期Demo

如下对某一个Bean进行getBean操作，最后销毁上下文，通过日志来查看SpringBean的生命周期

代码

package com.deepz.spring;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.beans.factory.support.MergedBeanDefinitionPostProcessor;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.env.Environment;
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

@Slf4j
@Configuration
public class BeanLifeCycleManager {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanLifeCycleManager.class);
        context.getBean("beanLifeCycle");
        context.close();
    }

    @Bean(initMethod = "init", destroyMethod = "destroyMethod")
    public BeanLifeCycle beanLifeCycle() {
        return new BeanLifeCycle();
    }

    interface MyAware extends ApplicationContextAware, EnvironmentAware, BeanFactoryAware {

    }

    @Component
    static class MyMergedBeanDefinitionPostProcessor implements MergedBeanDefinitionPostProcessor {

        @Override
        public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
            if ("beanLifeCycle".equals(beanName)) {
                log.info(">>>>>>>>>>元信息收集 ，MergedBeanDefinitionPostProcessor#postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) \nbeanDefinition = [{}]\n,beanType = [{}],beanName = [{}]\n", beanDefinition, beanType, beanName);
            }
        }
    }

    @Component
    static class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {
        @Override
        public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
            if ("beanLifeCycle".equals(beanName)) {
                log.info(">>>>>>>>>>实例化前，InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation(Class<?> beanClass,String beanName) \nbeanClass = [{}],beanName = [{}]\n", beanClass, beanName);
            }
            return null;
        }

        @Override
        public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
            if ("beanLifeCycle".equals(beanName)) {
                log.info(">>>>>>>>>>实例化后，InstantiationAwareBeanPostProcessor#postProcessAfterInstantiation(Object bean, String beanName)\nbean = [{}],beanName = [{}]\n", bean, beanName);
            }
            return false;
        }

        @Override
        public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
            if ("beanLifeCycle".equals(beanName)) {
                log.info(">>>>>>>>>>初始化前，InstantiationAwareBeanPostProcessor#postProcessBeforeInitialization(Object bean, String beanName)\nbean= [{}],beanName = [{}]\n", bean, beanName);
            }
            return bean;
        }

        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            if ("beanLifeCycle".equals(beanName)) {
                log.info(">>>>>>>>>>初始化后，InstantiationAwareBeanPostProcessor#postProcessAfterInitialization(Object bean, String beanName)\nbean= [{}],beanName = [{}]\n", bean, beanName);
            }
            return bean;
        }
    }

    public static class BeanLifeCycle implements InitializingBean, MyAware, DisposableBean {
        public void init() {
            log.info(">>>>>>>>>>init-method\n");
        }

        @PostConstruct
        public void postConstruct() {
            log.info(">>>>>>>>>>postConstruct\n");
        }

        @Override
        public void afterPropertiesSet() throws Exception {
            log.info(">>>>>>>>>>afterPropertiesSet\n");
        }

        public void destroyMethod() {
            log.info(">>>>>>>>>>destroy-method\n");
        }

        @Override
        public void destroy() {
            log.info(">>>>>>>>>>DisposableBean-destroy\n");
        }

        @PreDestroy
        public void preDestroy(){
            log.info(">>>>>>>>>>preDestroy\n");
        }


        @Override
        public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
            log.info(">>>>>>>>>>BeanFactoryAware#setBeanFactory\n");
        }

        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            log.info(">>>>>>>>>>ApplicationContextAware#setApplicationContext\n");
        }

        @Override
        public void setEnvironment(Environment environment) {
            log.info(">>>>>>>>>>EnvironmentAware#setEnvironment\n");
        }
    }
}

执行结果

实例化前

从createBean开始，见证Bean的实例化过程，首先是Bean实例化前的一个扩展点，它允许你自定义返回Bean实例。（AOP生成代理对象的入口之一，但基本不会走这里）

回调Bean实例化前的方法

AbstractAutowireCapableBeanFactory#createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)

主要是为了回调所有InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation(Class<?> beanClass, String beanName)方法，该方法会返回Object对象，如果返回的Object不为空，则会回调所有BeanPostProcessor的postProcessAfterInitialization(Object bean, String beanName)方法，那么返回的Object则会作为Bean去处理，如果返回Null，那么后续就会交由Spring来实例化、初始化（doCreateBean）。

自定义拦截实例化Bean后回调Bean后置方法

实例化

AbstractAutowireCapableBeanFactory#doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
如源码所示，如果上述扩展点没有return，那么就会进入到doCreateBean方法

首先是对Bean进行实例化，其中包括了构造器推断等，本文不过多聊这块内容，最后会返回BeanWrapper包裹的Bean实例。

元信息收集

实例化之后Spring通过回调MergedBeanDefinitionPostProcessor#postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName)对一些元信息做了收集维护处理，如@Autowire、@Resource、@PostConstruct 和 @PreDestroy等，为后续属性注入做准备。

MergedBeanDefinitionPostProcessor的实现类

MergedBeanDefinitionPostProcessor回调

初始化

实例化完了，对一些需要收集的信息也准备好了，后续就是进行属性注入和回调初始化方法了，其中populateBean方法是属性填充，initializeBean是回调初始化方法。

InstatiationAwareBeanPostProcessor回调postProcessAfterInstantiation方法

AbstractAutowireCapableBeanFactory#populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw)

Aware接口回调

AbstractAutowireCapableBeanFactory#initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd)

部分Aware接口回调、BeanPostProcessor的初始化前置回调(包括PostConstruct的调用、其余Aware的回调）、afterPropertiesSet回调、自定义init方法回调、BeanPostProcessor的初始化后置回调

部分Aware回调

AbstractAutowireCapableBeanFactory#invokeAwareMethods(final String beanName, final Object bean

BeanPostProcessor的初始化前置回调

重要BeanPostProcessor如下：

ApplicationContextAwareProcessor#postProcessBeforeInitialization(final Object bean, String beanName)回调剩余Aware方法

InitDestroyAnnotationBeanPostProcessor#postProcessBeforeInitialization(final Object bean, String beanName)回调PostConstruct方法

回调初始化方法

AbstractAutowireCapableBeanFactory#invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
先回调InitializingBean的afterPropertiesSet方法，随后回调自定义的init-method

BeanPostProcessor的初始化后置回调

注意：AOP生成代理的主要入口便是这里的了，对应的BeanPostProcessor->AbstractAutoProxyCreator。（后续单聊AOP相关源码，FLAG）

销毁

销毁方法最终会走到DisposableBeanAdapter的destroy方法去做处理，与初始化方法类似，这里简单介绍把。
看图就能发现，顺序执行的，先是注解方法，然后是DisposableBean的回调，最后是自定义的销毁方法，就是如此简单。

（小声）弄了挺久的，如果对你有帮助，或者让你回忆巩固相关知识点了，给我点个"支持“鼓励下..(滑稽），有什么问题欢迎评论讨论。。。