【死磕 Spring】----- 深入分析 ApplicationContext 的 refresh()

2021/6/26 23:29:49

编程Tag： class new spring refresh add ----- Bean BeanFactory ppName

本文主要是介绍【死磕 Spring】----- 深入分析 ApplicationContext 的 refresh()，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

原文:https://www.topjava.cn/category/1391374860344758272 『chenssy』

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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