Spring之SpringContext

一、概述

1.Spring Context概念

创建上下文并将BeanPostProcessor加载到spring

2.Spring Application Context概念

Spring通过应用上下文（Application Context）装载bean的定义并把它们组装起来。Spring应用上下文全权负责对象的创建和组装。

3. 关系

（1）Spring Context 模块核心是Spring Context

（2）Spring Context 核心是Spring Application Context

（3）Spring Application Context 的核心方法是 AbstractApplicationContext

二、AbstractApplicationContext之刷新源码分析

1. 基础源码

高效记忆：Spring应用文刷新 — 刷机

（1）手机系统太卡了于是自己刷机。首先 准备刷机环境 （准备刷新上下文环境），准备好后老系统 初始化并加载 定义信息（初始化BeanFactory，并加载bean definitions信息）

（2）然后进行系统 配置 并（对beanFacotry进行配置）开始系统 激活 并提交过程（激活BeanFactoryPostProcessors）

（3）再进行验证码 注册 并提交过程（注册BeanPostProcessors），注册后新系统 初始化信息资源、广播 且注册监听器（初始化MessageSource、初始化事件广播器、注册事件监听器）

（4）最后系统 热加载弹粒 并（构造热加载单例bean）完成刷机 （完成刷新过程,通知生命周期处理器），如果刷机 错误 就 销户并修改 激活标识（销毁bean、修改active标识）

@Overridepublicvoidrefresh()throwsBeansException,IllegalStateException{synchronized(this.startupShutdownMonitor){// Prepare this context for refreshing.prepareRefresh();// #1 准备刷新上下文环境// Tell the subclass to refresh the internal bean factory.ConfigurableListableBeanFactory beanFactory =obtainFreshBeanFactory();// #2 初始化BeanFactory，并加载bean definitions信息// Prepare the bean factory for use in this context.prepareBeanFactory(beanFactory);// #3 对beanFacotry进行配置try{// Allows post-processing of the bean factory in context subclasses.postProcessBeanFactory(beanFactory);// #4  提供给子类扩展的预留方法// Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory);// #5 激活BeanFactoryPostProcessors// Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory);// #6 注册BeanPostProcessors// Initialize message source for this context.initMessageSource();// #7 初始化MessageSource// Initialize event multicaster for this context.initApplicationEventMulticaster();// #8 初始化事件广播器// Initialize other special beans in specific context subclasses.onRefresh();// #9 提供给子类初始化其他的Bean// Check for listener beans and register them.registerListeners();// #10 注册事件监听器// Instantiate all remaining (non-lazy-init) singletons.finishBeanFactoryInitialization(beanFactory);// #11 构造热加载单例bean// Last step: publish corresponding event.finishRefresh();// #12 完成刷新过程,通知生命周期处理器}catch(BeansException ex){if(logger.isWarnEnabled()){
                    logger.warn("Exception encountered during context initialization - "+"cancelling refresh attempt: "+ ex);}// Destroy already created singletons to avoid dangling resources.destroyBeans();// #13 出错了，销毁bean// Reset 'active' flag.cancelRefresh(ex);// #14 出错了，修改active标识// Propagate exception to caller.throw ex;}finally{// Reset common introspection caches in Spring's core, since we// might not ever need metadata for singleton beans anymore...resetCommonCaches();}}}

2.初始化并加载 obtainFreshBeanFactory

AbstractApplicationContext—obtainFreshBeanFactory ----> AbstractRefreshableApplicationContext—refreshBeanFactory

protectedfinalvoidrefreshBeanFactory()throwsBeansException{if(hasBeanFactory()){// #1 如果已存在BeanFactory，销毁原来的BeanFactorydestroyBeans();closeBeanFactory();}try{DefaultListableBeanFactory beanFactory =createBeanFactory();// #2 创建DefaultListableBeanFactory
        beanFactory.setSerializationId(getId());customizeBeanFactory(beanFactory);// #3 加载bean definitions信息，loadBeanDefinitions是抽象方法，不同实现类会从不同的配置中获取bean definitions信息，// 如AnnotationConfigWebApplicationContext，XmlWebApplicationContext。loadBeanDefinitions(beanFactory);synchronized(this.beanFactoryMonitor){this.beanFactory = beanFactory;}}catch(IOException ex){thrownewApplicationContextException("I/O error parsing bean definition source for "+getDisplayName(), ex);}}

3.激活 BeanFactoryPostProcessors

（1）BeanFactoryPostProcessor是spring提供的扩展接口，可以通过BeanFactoryPostProcessor对beanFactory进行自定义处理，如修改其他BeanDefinition的配置。

（2）BeanFactoryPostProcessor可以调整beanFactory，甚至修改BeanDefinition，如CustomEditorConfigurer，将用户定义的PropertyEditor注册到beanFactory中，以便后续使用。

（3）BeanDefinitionRegistryPostProcessor可以注册新的BeanDefinition，如ConfigurationClassPostProcessor，是实现springboot很关键的类

AbstractApplicationContext—invokeBeanFactoryPostProcessors ----> PostProcessorRegistrationDelegate—invokeBeanFactoryPostProcessors

publicstaticvoidinvokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory,List<BeanFactoryPostProcessor> beanFactoryPostProcessors){Set<String> processedBeans =newHashSet<String>();// #1 如果beanFactory是BeanDefinitionRegistry，需要处理BeanFactoryPostProcessors，// BeanDefinitionRegistryPostProcessor，否则只处理BeanFactoryPostProcessorsif(beanFactory instanceofBeanDefinitionRegistry){BeanDefinitionRegistry registry =(BeanDefinitionRegistry) beanFactory;List<BeanFactoryPostProcessor> regularPostProcessors =newLinkedList<BeanFactoryPostProcessor>();List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =newLinkedList<BeanDefinitionRegistryPostProcessor>();// #2 方法参数beanFactoryPostProcessors是AbstractApplicationContext---beanFactoryPostProcessors属性，// 用户可以通过AbstractApplicationContext---addBeanFactoryPostProcessor方法添加BeanFactoryPostProcessor。这里对beanFactoryPostProcessors参数进行分类for(BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors){if(postProcessor instanceofBeanDefinitionRegistryPostProcessor){BeanDefinitionRegistryPostProcessor registryPostProcessor =(BeanDefinitionRegistryPostProcessor) postProcessor;
                registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                registryPostProcessors.add(registryPostProcessor);}else{
                regularPostProcessors.add(postProcessor);}}// #3 获取beanFactory已经存在的BeanDefinitionRegistryPostProcessor，这里并没有直接构建BeanDefinitionRegistryPostProcessor，而且通过beanName获取String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class,true,false);// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors =newArrayList<BeanDefinitionRegistryPostProcessor>();for(String ppName : postProcessorNames){if(beanFactory.isTypeMatch(ppName,PriorityOrdered.class)){
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName,BeanDefinitionRegistryPostProcessor.class));// #4 获取实现了PriorityOrdered接口的BeanDefinitionRegistryPostProcessor，添加到priorityOrderedPostProcessors     
                processedBeans.add(ppName);}}// #5 对priorityOrderedPostProcessors排序sortPostProcessors(beanFactory, priorityOrderedPostProcessors);// #6 排序结果添加到registryPostProcessors
        registryPostProcessors.addAll(priorityOrderedPostProcessors);// #7 调用BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistryinvokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class,true,false);List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors =newArrayList<BeanDefinitionRegistryPostProcessor>();for(String ppName : postProcessorNames){// #8 处理实现了Ordered的BeanDefinitionRegistryPostProcessorif(!processedBeans.contains(ppName)&& beanFactory.isTypeMatch(ppName,Ordered.class)){   
                orderedPostProcessors.add(beanFactory.getBean(ppName,BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);}}sortPostProcessors(beanFactory, orderedPostProcessors); 
        registryPostProcessors.addAll(orderedPostProcessors);invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.boolean reiterate =true;while(reiterate){
            reiterate =false;
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class,true,false);for(String ppName : postProcessorNames){// #9 处理剩余的BeanDefinitionRegistryPostProcessorif(!processedBeans.contains(ppName)){BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName,BeanDefinitionRegistryPostProcessor.class);
                    registryPostProcessors.add(pp);
                    processedBeans.add(ppName);
                    pp.postProcessBeanDefinitionRegistry(registry);
                    reiterate =true;}}}// Now, invoke the postProcessBeanFactory callback of all processors handled so far.invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);}...}

4.初始化事件广播 initApplicationEventMulticaster

4.1 Spring事件体系包括三个组件：

ApplicationEvent事件，ApplicationListener事件监听器，ApplicationEventMulticaster事件广播器。

4.2 事件广播器负责管理事件监听器，并将事件广播给监听器。

AbstractApplicationContext — initApplicationEventMulticaster

rotected voidinitApplicationEventMulticaster(){ConfigurableListableBeanFactory beanFactory =getBeanFactory();if(beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)){this.applicationEventMulticaster =
                beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME,ApplicationEventMulticaster.class);//#1 使用用户定义的事件广播器if(logger.isDebugEnabled()){
            logger.debug("Using ApplicationEventMulticaster ["+this.applicationEventMulticaster +"]");}}else{this.applicationEventMulticaster =newSimpleApplicationEventMulticaster(beanFactory);
        beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME,this.applicationEventMulticaster);//#2 使用默认的事件广播器if(logger.isDebugEnabled()){
            logger.debug("Unable to locate ApplicationEventMulticaster with name '"+APPLICATION_EVENT_MULTICASTER_BEAN_NAME+"': using default ["+this.applicationEventMulticaster +"]");}}}

4.3 spring事件

（1）spring提供了context start，stop，close，refresh等事件，ApplicationListener — onApplicationEvent负责处理spring中的事件。

（2）我们可以通过实现ApplicationListener接口自行处理事件，也可以通过PublishListener自定义事件监听器。

使用默认的事件广播器 AbstractApplicationContexton — publishEvent ----> SimpleApplicationEventMulticaster — multicastEvent

publicvoidmulticastEvent(finalApplicationEvent event,ResolvableType eventType){ResolvableType type =(eventType !=null? eventType :resolveDefaultEventType(event));for(finalApplicationListener<?> listener :getApplicationListeners(event, type)){Executor executor =getTaskExecutor();// #1 如果配置了Executor，使用Executor多线程处理if(executor !=null){
            executor.execute(newRunnable(){publicvoidrun(){invokeListener(listener, event);}});}else{invokeListener(listener, event);// #2 否则单线程处理}}}

5.注册事件监听器

AbstractApplicationContext — registerListeners将初始化事件监听器ApplicationListener，并绑定到事件广播器上。

protectedvoidregisterListeners(){for(ApplicationListener<?> listener :getApplicationListeners()){// #1 getApplicationListeners()获取的是AbstractApplicationContext --- applicationListeners，用户可以通过AbstractApplicationContext --- addApplicationListener添加事件监听器
将AbstractApplicationContext#applicationListeners注册到applicationEventMulticaster
        getApplicationEventMulticaster().addApplicationListener(listener);}String[] listenerBeanNames =getBeanNamesForType(ApplicationListener.class,true,false);// #2 将上下文中的ApplicationListener注册到applicationEventMulticasterfor(String listenerBeanName : listenerBeanNames){getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);}Set<ApplicationEvent> earlyEventsToProcess =this.earlyApplicationEvents;// #3 发布在此之前已发生的事件this.earlyApplicationEvents =null;if(earlyEventsToProcess !=null){for(ApplicationEvent earlyEvent : earlyEventsToProcess){getApplicationEventMulticaster().multicastEvent(earlyEvent);}}}

6.构造热加载单例bean

AbstractApplicationContext — finishBeanFactoryInitialization

protectedvoidfinishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory){// Initialize conversion service for this context.if(beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME)&&
            beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME,ConversionService.class)){
        beanFactory.setConversionService(
                beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME,ConversionService.class));//#1 初始化ConversionService，后面注入属性要使用}if(!beanFactory.hasEmbeddedValueResolver()){
        beanFactory.addEmbeddedValueResolver(newStringValueResolver(){//#2 初始化StringValueResolver，用于解析bean属性引用的properties配置@OverridepublicStringresolveStringValue(String strVal){returngetEnvironment().resolvePlaceholders(strVal);}});}String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class,false,false);//#3 初始化LoadTimeWeaverAwarefor(String weaverAwareName : weaverAwareNames){getBean(weaverAwareName);}

    beanFactory.setTempClassLoader(null);

    beanFactory.freezeConfiguration();// Instantiate all remaining (non-lazy-init) singletons.
    beanFactory.preInstantiateSingletons();//#4 构造热加载单例bean}

AbstractApplicationContext — preInstantiateSingletons

publicvoidpreInstantiateSingletons()throwsBeansException{...List<String> beanNames =newArrayList<String>(this.beanDefinitionNames);for(String beanName : beanNames){RootBeanDefinition bd =getMergedLocalBeanDefinition(beanName);if(!bd.isAbstract()&& bd.isSingleton()&&!bd.isLazyInit()){// #1 判断是否为非抽象类的热加载单例beanif(isFactoryBean(beanName)){finalFactoryBean<?> factory =(FactoryBean<?>)getBean(FACTORY_BEAN_PREFIX+ beanName);boolean isEagerInit;if(System.getSecurityManager()!=null&& factory instanceofSmartFactoryBean){
                        isEagerInit =AccessController.doPrivileged(newPrivilegedAction<Boolean>(){@OverridepublicBooleanrun(){return((SmartFactoryBean<?>) factory).isEagerInit();}},getAccessControlContext());}else{
                        isEagerInit =(factory instanceofSmartFactoryBean&&((SmartFactoryBean<?>) factory).isEagerInit());}if(isEagerInit){getBean(beanName);}}else{getBean(beanName);// #2 构造bean：如果非FactoryBean，构造bean。如果FactoryBean并且FactoryBean.isEagerInit为true，构造bean。}}}...}

7. 完成刷新 finishRefresh

LifecycleProcessor也是spring提供的扩展点， 通过它可以在spring content start，stop，onRefresh等时刻自定义一些额外操作

protectedvoidfinishRefresh(){// Initialize lifecycle processor for this context.initLifecycleProcessor();// #1 初始化LifecycleProcessor// Propagate refresh to lifecycle processor first.getLifecycleProcessor().onRefresh();// #2 调用LifecycleProcessor#onRefresh()方法// Publish the final event.publishEvent(newContextRefreshedEvent(this));// #3 发布事件// Participate in LiveBeansView MBean, if active.LiveBeansView.registerApplicationContext(this);}

参考链接1

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