/** Synchronization monitor for the "refresh" and "destroy" */
	//refresh(),close(),registerShutdownHook()方法
	private final Object startupShutdownMonitor = new Object();
@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      // Prepare this context for refreshing.
     /**
      * 表示真正做refresh之前需要做的事情：
      * 1. 设置Spring容器的启动时间，撤销关闭状态，开启活跃状态
      * 2. 初始化property
      * 3. 验证环境信息里必须存在的属性
      */
      prepareRefresh();
      // Tell the subclass to refresh the internal bean factory.
      // 主要是解析我们项目配置的application.xml、xxx.xml 定义的import、bean、resource、profile等
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
      // Prepare the bean factory for use in this context.
      /**
       * 对beanFactory进行相关设置，为后续的使用做准备
       */
      prepareBeanFactory(beanFactory);
      try {
         // Allows post-processing of the bean factory in context subclasses.
        /**
			   * 子类覆盖方法做额外的处理
			   * BeanFactory设置之后再进行后续的一些BeanFactory操作
			   * 不同的Spring容器做不同的操作。比如GenericWebApplicationContext容器会在BeanFactory中添加
			   * ServletContextAwareProcessor用于处理ServletContextAware类型的bean初始化的时候调用
			   * setServletContext或者setServletConfig方法
			   * (跟ApplicationContextAwareProcessor原理一样)
			   */	
         postProcessBeanFactory(beanFactory);
         /** 
         	* Invoke factory processors registered as beans in the context.
         	* 激活各种BeanFactory处理器
         	*/、
         
         invokeBeanFactoryPostProcessors(beanFactory);
         /**
          * Register bean processors that intercept bean creation.
          * 注册拦截 Bean 创建的 Bean 处理器，这里只是注册，真正的调用是在 getBean 时候
          */
         registerBeanPostProcessors(beanFactory);
         /* 为上下文初始化 Message 源，即不同语言的消息体，国际化处理
          * Initialize message source for this context.
          */
         initMessageSource();
         // Initialize event multicaster for this context.
         initApplicationEventMulticaster();
         // Initialize other special beans in specific context subclasses.
         onRefresh();
         // Check for listener beans and register them.
         registerListeners();
         // Instantiate all remaining (non-lazy-init) singletons.
         finishBeanFactoryInitialization(beanFactory);
         // Last step: publish corresponding event.
         finishRefresh();
      }
      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();
         // Reset 'active' flag.
         cancelRefresh(ex);
         // 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();
      }
   }
}