深入分析ApplicationContext的refresh()

2020-01-26 Spring 《Spring源码分析》

本文作者:chenssy

出处:http://cmsblogs.com/?p=4043

在学习Spring源码的过程中发现的好站+好贴,原创不易感谢作者。

Spring版本:Spring 5.0.6.RELEASE

上篇博客对 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);
}
Spring 死磕Spring

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