@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// 刷新前的准备工作
			// Prepare this context for refreshing.
			prepareRefresh();

			// 获取子类刷新后的内部 beanFactory 实例
			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// 为容器注册必要的系统级别的 bean
			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// 允许容器的子类去注册 postProcessor
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// 调用容器注册的容器级别的后置处理器
				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// 向容器注册 bean 级别的后置处理器
				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// 初始化国际化配置
				// Initialize message source for this context.
				initMessageSource();

				// 初始化事件发布器组件
				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// 在单例 bean 初始化之前预留给子类初始化其他 bean 的口子
				// 例如如果是 web 应用，其中完成内嵌 web 容器的创建
				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// 向前面的事件发布器组件注册事件监听器
				// Check for listener beans and register them.
				registerListeners();

				// 设置系统级别的服务，实例化所有非懒加载的单例
				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// 触发初始化完成的回调方法，并发布容器刷新完成的事件给监听者
				// 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 {
				// 重置 Spring 内核中的公共缓存
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}