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作者 | DeepSleeping丶

來源 | urlify.cn/jy6NJr

概述

本文描述下Spring的實(shí)例化、初始化、銷毀，整個(gè)SpringBean生命周期，聊一聊BeanPostProcessor的回調(diào)時(shí)機(jī)、Aware方法的回調(diào)時(shí)機(jī)、初始化方法的回調(diào)及其順序、銷毀方法的回調(diào)及其順序、重要的BeanPostProcessor的介紹。
開頭是一張我畫的調(diào)用流轉(zhuǎn)圖，然后就是我寫的一個(gè)Demo通過日志打印了SpringBean的生命周期，最后通過源碼慢慢跟進(jìn)其生命周期。

生命周期流轉(zhuǎn)圖

生命周期Demo

如下對(duì)某一個(gè)Bean進(jìn)行g(shù)etBean操作，最后銷毀上下文，通過日志來查看SpringBean的生命周期

代碼

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(">>>>>>>>>>實(shí)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(">>>>>>>>>>實(shí)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");
        }
    }
}

執(zhí)行結(jié)果

實(shí)例化前

從createBean開始，見證Bean的實(shí)例化過程，首先是Bean實(shí)例化前的一個(gè)擴(kuò)展點(diǎn)，它允許你自定義返回Bean實(shí)例。（AOP生成代理對(duì)象的入口之一，但基本不會(huì)走這里）

回調(diào)Bean實(shí)例化前的方法

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

主要是為了回調(diào)所有InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation(Class<?> beanClass, String beanName)方法，該方法會(huì)返回Object對(duì)象，如果返回的Object不為空，則會(huì)回調(diào)所有BeanPostProcessor的postProcessAfterInitialization(Object bean, String beanName)方法，那么返回的Object則會(huì)作為Bean去處理，如果返回Null，那么后續(xù)就會(huì)交由Spring來實(shí)例化、初始化（doCreateBean）。

自定義攔截實(shí)例化Bean后回調(diào)Bean后置方法

實(shí)例化

AbstractAutowireCapableBeanFactory#doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
如源碼所示，如果上述擴(kuò)展點(diǎn)沒有return，那么就會(huì)進(jìn)入到doCreateBean方法

首先是對(duì)Bean進(jìn)行實(shí)例化，其中包括了構(gòu)造器推斷等，本文不過多聊這塊內(nèi)容，最后會(huì)返回BeanWrapper包裹的Bean實(shí)例。

元信息收集

實(shí)例化之后Spring通過回調(diào)MergedBeanDefinitionPostProcessor#postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName)對(duì)一些元信息做了收集維護(hù)處理，如@Autowire、@Resource、@PostConstruct 和 @PreDestroy等，為后續(xù)屬性注入做準(zhǔn)備。

MergedBeanDefinitionPostProcessor的實(shí)現(xiàn)類

MergedBeanDefinitionPostProcessor回調(diào)

初始化

實(shí)例化完了，對(duì)一些需要收集的信息也準(zhǔn)備好了，后續(xù)就是進(jìn)行屬性注入和回調(diào)初始化方法了，其中populateBean方法是屬性填充，initializeBean是回調(diào)初始化方法。

InstatiationAwareBeanPostProcessor回調(diào)postProcessAfterInstantiation方法

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

Aware接口回調(diào)

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

部分Aware接口回調(diào)、BeanPostProcessor的初始化前置回調(diào)(包括PostConstruct的調(diào)用、其余Aware的回調(diào)）、afterPropertiesSet回調(diào)、自定義init方法回調(diào)、BeanPostProcessor的初始化后置回調(diào)

部分Aware回調(diào)

AbstractAutowireCapableBeanFactory#invokeAwareMethods(final String beanName, final Object bean

BeanPostProcessor的初始化前置回調(diào)

重要BeanPostProcessor如下：

ApplicationContextAwareProcessor#postProcessBeforeInitialization(final Object bean, String beanName)回調(diào)剩余Aware方法

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

回調(diào)初始化方法

AbstractAutowireCapableBeanFactory#invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
先回調(diào)InitializingBean的afterPropertiesSet方法，隨后回調(diào)自定義的init-method

BeanPostProcessor的初始化后置回調(diào)

注意：AOP生成代理的主要入口便是這里的了，對(duì)應(yīng)的BeanPostProcessor->AbstractAutoProxyCreator。（后續(xù)單聊AOP相關(guān)源碼，F(xiàn)LAG）

銷毀

銷毀方法最終會(huì)走到DisposableBeanAdapter的destroy方法去做處理，與初始化方法類似，這里簡單介紹把。
看圖就能發(fā)現(xiàn)，順序執(zhí)行的，先是注解方法，然后是DisposableBean的回調(diào)，最后是自定義的銷毀方法，就是如此簡單。

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深入源碼理解SpringBean生命周期

概述