深入源码理解SpringBean生命周期

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2021-05-20 23:02

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  作者 |  DeepSleeping丶

来源 |  urlify.cn/jy6NJr

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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。





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