2021-05-09 20:52  阅读(17373)
文章分类:死磕 Spring 之 IOC 文章标签:死磕 Java死磕 SpringSpring 源码
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上篇博客只是对 ApplicationContext 相关的接口做了一个简单的介绍,作为一个高富帅级别的 Spring 容器,它涉及的方法实在是太多了,全部介绍是不可能的,而且大部分功能都已经在前面系列博客中做了详细的介绍,所以这篇博问介绍 ApplicationContext 最重要的方法(小编认为的) :refresh()

refresh() 是定义在 ConfigurableApplicationContext 类中的,如下:

        /**
         * Load or refresh the persistent representation of the configuration,
         * which might an XML file, properties file, or relational database schema.
         * As this is a startup method, it should destroy already created singletons
         * if it fails, to avoid dangling resources. In other words, after invocation
         * of that method, either all or no singletons at all should be instantiated.
         * @throws BeansException if the bean factory could not be initialized
         * @throws IllegalStateException if already initialized and multiple refresh
         * attempts are not supported
         */
        void refresh() throws BeansException, IllegalStateException;
    

作用就是:刷新 Spring 的应用上下文。其实现是在 AbstractApplicationContext 中实现。如下:

        @Override
        public void refresh() throws BeansException, IllegalStateException {
            synchronized (this.startupShutdownMonitor) {
                // 准备刷新上下文环境
                prepareRefresh();
    
                // 创建并初始化 BeanFactory
                ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
                // 填充BeanFactory功能
                prepareBeanFactory(beanFactory);
    
                try {
                    // 提供子类覆盖的额外处理,即子类处理自定义的BeanFactoryPostProcess
                    postProcessBeanFactory(beanFactory);
    
                    // 激活各种BeanFactory处理器
                    invokeBeanFactoryPostProcessors(beanFactory);
    
                    // 注册拦截Bean创建的Bean处理器,即注册 BeanPostProcessor
                    registerBeanPostProcessors(beanFactory);
    
                    // 初始化上下文中的资源文件,如国际化文件的处理等
                    initMessageSource();
    
                    // 初始化上下文事件广播器
                    initApplicationEventMulticaster();
    
                    // 给子类扩展初始化其他Bean
                    onRefresh();
    
                    // 在所有bean中查找listener bean,然后注册到广播器中
                    registerListeners();
    
                    // 初始化剩下的单例Bean(非延迟加载的)
                    finishBeanFactoryInitialization(beanFactory);
    
                    // 完成刷新过程,通知生命周期处理器lifecycleProcessor刷新过程,同时发出ContextRefreshEvent通知别人
                    finishRefresh();
                }
    
                catch (BeansException ex) {
                    if (logger.isWarnEnabled()) {
                        logger.warn("Exception encountered during context initialization - " +
                                "cancelling refresh attempt: " + ex);
                    }
    
                    //  销毁已经创建的Bean
                    destroyBeans();
    
                    // 重置容器激活标签
                    cancelRefresh(ex);
    
                    // 抛出异常
                    throw ex;
                }
    
                finally {
                    // Reset common introspection caches in Spring's core, since we
                    // might not ever need metadata for singleton beans anymore...
                    resetCommonCaches();
                }
            }
        }
    

这里每一个方法都非常重要,需要一个一个地解释说明。

prepareRefresh()

初始化上下文环境,对系统的环境变量或者系统属性进行准备和校验,如环境变量中必须设置某个值才能运行,否则不能运行,这个时候可以在这里加这个校验,重写initPropertySources方法就好了

        protected void prepareRefresh() {
           // 设置启动日期
            this.startupDate = System.currentTimeMillis();
            // 设置 context 当前状态
            this.closed.set(false);
            this.active.set(true);
    
            if (logger.isInfoEnabled()) {
                logger.info("Refreshing " + this);
            }
    
            // 初始化context environment(上下文环境)中的占位符属性来源
            initPropertySources();
    
            // 对属性进行必要的验证
            getEnvironment().validateRequiredProperties();
    
            this.earlyApplicationEvents = new LinkedHashSet<>();
        }
    

该方法主要是做一些准备工作,如:

  1. 设置 context 启动时间
  2. 设置 context 的当前状态
  3. 初始化 context environment 中占位符
  4. 对属性进行必要的验证

obtainFreshBeanFactory()

创建并初始化 BeanFactory

        protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
           // 刷新 BeanFactory
            refreshBeanFactory();
            // 获取 BeanFactory
            ConfigurableListableBeanFactory beanFactory = getBeanFactory();
            if (logger.isDebugEnabled()) {
                logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
            }
            return beanFactory;
        }
    

核心方法就在 refreshBeanFactory() ,该方法的核心任务就是创建 BeanFactory 并对其就行一番初始化。如下:

        protected final void refreshBeanFactory() throws BeansException {
            if (hasBeanFactory()) {
                destroyBeans();
                closeBeanFactory();
            }
            try {
                DefaultListableBeanFactory beanFactory = createBeanFactory();
                beanFactory.setSerializationId(getId());
                customizeBeanFactory(beanFactory);
                loadBeanDefinitions(beanFactory);
                synchronized (this.beanFactoryMonitor) {
                    this.beanFactory = beanFactory;
                }
            }
            catch (IOException ex) {
                throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
            }
        }
    
  1. 判断当前容器是否存在一个 BeanFactory,如果存在则对其进行销毁和关闭
  2. 调用 createBeanFactory() 创建一个 BeanFactory 实例,其实就是 DefaultListableBeanFactory
  3. 自定义 BeanFactory
  4. 加载 BeanDefinition
  5. 将创建好的 bean 工厂的引用交给的 context 来管理

上面 5 个步骤,都是比较简单的,但是有必要讲解下第 4 步:加载 BeanDefinition。如果各位看过 【死磕 Spring】系列的话,在刚刚开始分析源码的时候,小编就是以 loadBeanDefinitions() 为入口来分析的,如下:

    ClassPathResource resource = new ClassPathResource("bean.xml");
    DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
    XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
    reader.loadBeanDefinitions(resource);
    

只不过这段代码的 loadBeanDefinitions() 是定义在 BeanDefinitionReader 中,而此处的 loadBeanDefinitions() 则是定义在 AbstractRefreshableApplicationContext 中,如下:

        protected abstract void loadBeanDefinitions(DefaultListableBeanFactory beanFactory)
                throws BeansException, IOException
    

由具体的子类实现,我们以 AbstractXmlApplicationContext 为例,实现如下:

        protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
            // Create a new XmlBeanDefinitionReader for the given BeanFactory.
            XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
    
            // Configure the bean definition reader with this context's
            // resource loading environment.
            beanDefinitionReader.setEnvironment(this.getEnvironment());
            beanDefinitionReader.setResourceLoader(this);
            beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
    
            // Allow a subclass to provide custom initialization of the reader,
            // then proceed with actually loading the bean definitions.
            initBeanDefinitionReader(beanDefinitionReader);
            loadBeanDefinitions(beanDefinitionReader);
        }
    

新建 XmlBeanDefinitionReader 实例对象 beanDefinitionReader,调用 initBeanDefinitionReader() 对其进行初始化,然后调用 loadBeanDefinitions() 加载 BeanDefinition。

        protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
            Resource[] configResources = getConfigResources();
            if (configResources != null) {
                reader.loadBeanDefinitions(configResources);
            }
            String[] configLocations = getConfigLocations();
            if (configLocations != null) {
                reader.loadBeanDefinitions(configLocations);
            }
        }
    

到这里我们发现,其实内部依然是调用 BeanDefinitionReader#loadBeanDefinitionn() 进行 BeanDefinition 的加载进程。

prepareBeanFactory(beanFactory)

填充 BeanFactory 功能

上面获取获取的 BeanFactory 除了加载了一些 BeanDefinition 就没有其他任何东西了,这个时候其实还不能投入生产,因为还少配置了一些东西,比如 context的 ClassLoader 和 后置处理器等等。

        protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
            // 设置beanFactory的classLoader
            beanFactory.setBeanClassLoader(getClassLoader());
    
            // 设置beanFactory的表达式语言处理器,Spring3开始增加了对语言表达式的支持,默认可以使用#{bean.xxx}的形式来调用相关属性值
            beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
            // 为beanFactory增加一个默认的propertyEditor
            beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
    
            // 添加ApplicationContextAwareProcessor
            beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
            // 设置忽略自动装配的接口
            beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
            beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
            beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
            beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
            beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
            beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
    
            // 设置几个自动装配的特殊规则
            beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
            beanFactory.registerResolvableDependency(ResourceLoader.class, this);
            beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
            beanFactory.registerResolvableDependency(ApplicationContext.class, this);
    
            // Register early post-processor for detecting inner beans as ApplicationListeners.
            beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
    
            // 增加对AspectJ的支持
            if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
                beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
                // Set a temporary ClassLoader for type matching.
                beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
            }
    
            // 注册默认的系统环境bean
            if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
                beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
            }
            if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
                beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
            }
            if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
                beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
            }
        }
    

看上面的源码知道这个就是对 BeanFactory 设置各种各种的功能。

postProcessBeanFactory()

提供子类覆盖的额外处理,即子类处理自定义的BeanFactoryPostProcess

        protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
            beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
            beanFactory.ignoreDependencyInterface(ServletContextAware.class);
            beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
    
            WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
            WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
        }
    
  1. 添加 ServletContextAwareProcessor 到 BeanFactory 容器中,该 processor 实现 BeanPostProcessor 接口,主要用于将ServletContext 传递给实现了 ServletContextAware 接口的 bean
  2. 忽略 ServletContextAware、ServletConfigAware
  3. 注册 WEB 应用特定的域(scope)到 beanFactory 中,以便 WebApplicationContext 可以使用它们。比如 "request" , "session" , "globalSession" , "application"
  4. 注册 WEB 应用特定的 Environment bean 到 beanFactory 中,以便WebApplicationContext 可以使用它们。如:"contextParameters", "contextAttributes"

invokeBeanFactoryPostProcessors()

激活各种BeanFactory处理器

        public static void invokeBeanFactoryPostProcessors(
                ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
    
            // 定义一个 set 保存所有的 BeanFactoryPostProcessors
            Set<String> processedBeans = new HashSet<>();
    
            // 如果当前 BeanFactory 为 BeanDefinitionRegistry
            if (beanFactory instanceof BeanDefinitionRegistry) {
                BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
                // BeanFactoryPostProcessor 集合
                List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
                // BeanDefinitionRegistryPostProcessor 集合
                List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
    
                // 迭代注册的 beanFactoryPostProcessors
                for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
                    // 如果是 BeanDefinitionRegistryPostProcessor,则调用 postProcessBeanDefinitionRegistry 进行注册,
                    // 同时加入到 registryProcessors 集合中
                    if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                        BeanDefinitionRegistryPostProcessor registryProcessor =
                                (BeanDefinitionRegistryPostProcessor) postProcessor;
                        registryProcessor.postProcessBeanDefinitionRegistry(registry);
                        registryProcessors.add(registryProcessor);
                    }
                    else {
                        // 否则当做普通的 BeanFactoryPostProcessor 处理
                        // 添加到 regularPostProcessors 集合中即可,便于后面做后续处理
                        regularPostProcessors.add(postProcessor);
                    }
                }
    
                // 用于保存当前处理的 BeanDefinitionRegistryPostProcessor
                List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
    
                // 首先处理实现了 PriorityOrdered (有限排序接口)的 BeanDefinitionRegistryPostProcessor
                String[] postProcessorNames =
                        beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                for (String ppName : postProcessorNames) {
                    if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                        currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                        processedBeans.add(ppName);
                    }
                }
    
                // 排序
                sortPostProcessors(currentRegistryProcessors, beanFactory);
    
                // 加入registryProcessors集合
                registryProcessors.addAll(currentRegistryProcessors);
    
                // 调用所有实现了 PriorityOrdered 的 BeanDefinitionRegistryPostProcessors 的 postProcessBeanDefinitionRegistry()
                invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    
                // 清空,以备下次使用
                currentRegistryProcessors.clear();
    
                // 其次,调用是实现了 Ordered(普通排序接口)的 BeanDefinitionRegistryPostProcessors
                // 逻辑和 上面一样
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                for (String ppName : postProcessorNames) {
                    if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                        currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                        processedBeans.add(ppName);
                    }
                }
                sortPostProcessors(currentRegistryProcessors, beanFactory);
                registryProcessors.addAll(currentRegistryProcessors);
                invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
                currentRegistryProcessors.clear();
    
                // 最后调用其他的 BeanDefinitionRegistryPostProcessors
                boolean reiterate = true;
                while (reiterate) {
                    reiterate = false;
                    // 获取 BeanDefinitionRegistryPostProcessor
                    postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                    for (String ppName : postProcessorNames) {
    
                        // 没有包含在 processedBeans 中的(因为包含了的都已经处理了)
                        if (!processedBeans.contains(ppName)) {
                            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                            processedBeans.add(ppName);
                            reiterate = true;
                        }
                    }
    
                    // 与上面处理逻辑一致
                    sortPostProcessors(currentRegistryProcessors, beanFactory);
                    registryProcessors.addAll(currentRegistryProcessors);
                    invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
                    currentRegistryProcessors.clear();
                }
    
                // 调用所有 BeanDefinitionRegistryPostProcessor (包括手动注册和通过配置文件注册)
                // 和 BeanFactoryPostProcessor(只有手动注册)的回调函数(postProcessBeanFactory())
                invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
                invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
            }
    
            else {
                // 如果不是 BeanDefinitionRegistry 只需要调用其回调函数(postProcessBeanFactory())即可
                invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
            }
    
            //
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
    
            // 这里同样需要区分 PriorityOrdered 、Ordered 和 no Ordered
            List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
            List<String> orderedPostProcessorNames = new ArrayList<>();
            List<String> nonOrderedPostProcessorNames = new ArrayList<>();
            for (String ppName : postProcessorNames) {
                // 已经处理过了的,跳过
                if (processedBeans.contains(ppName)) {
                    // skip - already processed in first phase above
                }
                // PriorityOrdered
                else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
                }
                // Ordered
                else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    orderedPostProcessorNames.add(ppName);
                }
                // no Ordered
                else {
                    nonOrderedPostProcessorNames.add(ppName);
                }
            }
    
            // First, PriorityOrdered 接口
            sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
    
            // Next, Ordered 接口
            List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
            for (String postProcessorName : orderedPostProcessorNames) {
                orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
            }
            sortPostProcessors(orderedPostProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
    
            // Finally, no ordered
            List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
            for (String postProcessorName : nonOrderedPostProcessorNames) {
                nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
            }
            invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
    
            // Clear cached merged bean definitions since the post-processors might have
            // modified the original metadata, e.g. replacing placeholders in values...
            beanFactory.clearMetadataCache();
        }
    

上述代码较长,但是处理逻辑较为单一,就是对所有的 BeanDefinitionRegistryPostProcessors 、手动注册的 BeanFactoryPostProcessor 以及通过配置文件方式的 BeanFactoryPostProcessor 按照 PriorityOrdered 、 Ordered、no ordered 三种方式分开处理、调用。

registerBeanPostProcessors

注册拦截Bean创建的Bean处理器,即注册 BeanPostProcessor

与 BeanFactoryPostProcessor 一样,也是委托给 PostProcessorRegistrationDelegate 来实现的。

        public static void registerBeanPostProcessors(
                ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
    
            // 所有的 BeanPostProcessors
            String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
    
            // 注册 BeanPostProcessorChecker
            // 主要用于记录一些 bean 的信息,这些 bean 不符合所有 BeanPostProcessors 处理的资格时
            int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
            beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    
            // 区分 PriorityOrdered、Ordered 、 no ordered
            List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
            List<String> orderedPostProcessorNames = new ArrayList<>();
            List<String> nonOrderedPostProcessorNames = new ArrayList<>();
            // MergedBeanDefinition
            List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
            for (String ppName : postProcessorNames) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                    priorityOrderedPostProcessors.add(pp);
                    if (pp instanceof MergedBeanDefinitionPostProcessor) {
                        internalPostProcessors.add(pp);
                    }
                }
                else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    orderedPostProcessorNames.add(ppName);
                }
                else {
                    nonOrderedPostProcessorNames.add(ppName);
                }
            }
    
            // First, PriorityOrdered
            sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
            registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
    
            // Next, Ordered
            List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
            for (String ppName : orderedPostProcessorNames) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                orderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            sortPostProcessors(orderedPostProcessors, beanFactory);
            registerBeanPostProcessors(beanFactory, orderedPostProcessors);
    
            // onOrdered
            List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
            for (String ppName : nonOrderedPostProcessorNames) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                nonOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
    
            // Finally, all internal BeanPostProcessors.
            sortPostProcessors(internalPostProcessors, beanFactory);
            registerBeanPostProcessors(beanFactory, internalPostProcessors);
    
            // 重新注册用来自动探测内部ApplicationListener的post-processor,这样可以将他们移到处理器链条的末尾
            beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
        }
    

initMessageSource

初始化上下文中的资源文件,如国际化文件的处理等

其实该方法就是初始化一个 MessageSource 接口的实现类,主要用于国际化/i18n。

        protected void initMessageSource() {
            ConfigurableListableBeanFactory beanFactory = getBeanFactory();
            // 包含 “messageSource” bean
            if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
                this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
                // 如果有父类
                // HierarchicalMessageSource 分级处理的 MessageSource
                if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
                    HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
                    if (hms.getParentMessageSource() == null) {
                        // 如果没有注册父 MessageSource,则设置为父类上下文的的 MessageSource
                        hms.setParentMessageSource(getInternalParentMessageSource());
                    }
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Using MessageSource [" + this.messageSource + "]");
                }
            }
            else {
                // 使用 空 MessageSource
                DelegatingMessageSource dms = new DelegatingMessageSource();
                dms.setParentMessageSource(getInternalParentMessageSource());
                this.messageSource = dms;
                beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
                if (logger.isDebugEnabled()) {
                    logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
                            "': using default [" + this.messageSource + "]");
                }
            }
        }
    

initApplicationEventMulticaster

初始化上下文事件广播器

        protected void initApplicationEventMulticaster() {
            ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    
            // 如果存在 applicationEventMulticaster bean,则获取赋值
            if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
                this.applicationEventMulticaster =
                        beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
                if (logger.isDebugEnabled()) {
                    logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
                }
            }
            else {
                // 没有则新建 SimpleApplicationEventMulticaster,并完成 bean 的注册
                this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
                beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
                if (logger.isDebugEnabled()) {
                    logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
                            APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
                            "': using default [" + this.applicationEventMulticaster + "]");
                }
            }
        }
    

如果当前容器中存在 applicationEventMulticaster 的 bean,则对 applicationEventMulticaster 赋值,否则新建一个 SimpleApplicationEventMulticaster 的对象(默认的),并完成注册。

onRefresh

给子类扩展初始化其他Bean

预留给 AbstractApplicationContext 的子类用于初始化其他特殊的 bean,该方法需要在所有单例 bean 初始化之前调用。

registerListeners

在所有 bean 中查找 listener bean,然后注册到广播器中

        protected void registerListeners() {
            // 注册静态 监听器
            for (ApplicationListener<?> listener : getApplicationListeners()) {
                getApplicationEventMulticaster().addApplicationListener(listener);
            }
    
            String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
            for (String listenerBeanName : listenerBeanNames) {
                getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
            }
    
            // 至此,已经完成将监听器注册到ApplicationEventMulticaster中,下面将发布前期的事件给监听器。
            Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
            this.earlyApplicationEvents = null;
            if (earlyEventsToProcess != null) {
                for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                    getApplicationEventMulticaster().multicastEvent(earlyEvent);
                }
            }
        }
    

finishBeanFactoryInitialization

初始化剩下的单例Bean(非延迟加载的)

        protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
            // 初始化转换器
            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));
            }
    
            // 如果之前没有注册 bean 后置处理器(例如PropertyPlaceholderConfigurer),则注册默认的解析器
            if (!beanFactory.hasEmbeddedValueResolver()) {
                beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
            }
    
            // 初始化 Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
            String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
            for (String weaverAwareName : weaverAwareNames) {
                getBean(weaverAwareName);
            }
    
            // 停止使用临时的 ClassLoader
            beanFactory.setTempClassLoader(null);
    
            //
            beanFactory.freezeConfiguration();
    
            // 初始化所有剩余的单例(非延迟初始化)
            beanFactory.preInstantiateSingletons();
        }
    

finishRefresh

完成刷新过程,通知生命周期处理器 lifecycleProcessor 刷新过程,同时发出 ContextRefreshEvent 通知别人

主要是调用 LifecycleProcessor#onRefresh() ,并且发布事件(ContextRefreshedEvent)。

        protected void finishRefresh() {
            // Clear context-level resource caches (such as ASM metadata from scanning).
            clearResourceCaches();
    
            // Initialize lifecycle processor for this context.
            initLifecycleProcessor();
    
            // Propagate refresh to lifecycle processor first.
            getLifecycleProcessor().onRefresh();
    
            // Publish the final event.
            publishEvent(new ContextRefreshedEvent(this));
    
            // Participate in LiveBeansView MBean, if active.
            LiveBeansView.registerApplicationContext(this);
        }
    
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