public void refresh() throws BeansException, IllegalStateException {
 synchronized (this.startupShutdownMonitor) {
  //刷新之前的准备工作，包括设置启动时间，是否激活标识位，初始化属性源(property source)配置
  prepareRefresh();
  //由子类去刷新BeanFactory(如果还没创建则创建)，并将BeanFactory返回
  ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
  //准备BeanFactory以供ApplicationContext使用
  prepareBeanFactory(beanFactory);
  try {
   //子类可通过格式此方法来对BeanFactory进行修改
   postProcessBeanFactory(beanFactory);
   //实例化并调用所有注册的BeanFactoryPostProcessor对象
   invokeBeanFactoryPostProcessors(beanFactory);
   //实例化并调用所有注册的BeanPostProcessor对象
   registerBeanPostProcessors(beanFactory);
   //初始化MessageSource
   initMessageSource();
   //初始化事件广播器
   initApplicationEventMulticaster();
   //子类覆盖此方法在刷新过程做额外工作
   onRefresh();
   //注册应用监听器ApplicationListener
   registerListeners();
   //实例化所有non-lazy-init bean
   finishBeanFactoryInitialization(beanFactory);
   //刷新完成工作，包括初始化LifecycleProcessor，发布刷新完成事件等
   finishRefresh();
  }
  catch (BeansException ex) {
   // Destroy already created singletons to avoid dangling resources.
   destroyBeans();
   // Reset 'active' flag.
   cancelRefresh(ex);
   // Propagate exception to caller.
   throw ex;
  }
 }
}

protected void finishRefresh() {
 // //初始化LifecycleProcessor
 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);
}

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

@Override
protected final void refreshBeanFactory() throws BeansException {
  if (hasBeanFactory()) {//如果beanFactory已经不为null，则销毁beanFactory中的Bean后自行关闭
    destroyBeans();
    closeBeanFactory();
  }
  try {
    DefaultListableBeanFactory beanFactory = createBeanFactory();//创建beanFactory
    beanFactory.setSerializationId(getId());
    customizeBeanFactory(beanFactory);
    loadBeanDefinitions(beanFactory);
    synchronized (this.beanFactoryMonitor) {
      this.beanFactory = beanFactory;//对beanFactory成员进行赋值
    }
  }
  catch (IOException ex) {
    throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
  }
}

protected void initApplicationEventMulticaster() {
  ConfigurableListableBeanFactory beanFactory = getBeanFactory();
  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 {
    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 + "]");
    }
  }
}

1. public static void main(String[] args) {
  ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext();
  applicationContext.setConfigLocation("application-context.xml");
  applicationContext.start();
  applicationContext.close();
}
2. public static void main(String[] args) {
  ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext();
  applicationContext.setConfigLocation("application-context.xml");
  applicationContext.getBean("xtayfjpk");
  applicationContext.close();
}
3. public static void main(String[] args) {
  GenericApplicationContext parent = new GenericApplicationContext();
  AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
  context.setParent(parent);
  context.refresh();
  context.start();
  context.close();
}

public void start() {
  getLifecycleProcessor().start();
  publishEvent(new ContextStartedEvent(this));
}

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
  super(parent);
  setConfigLocations(configLocations);
  if (refresh) {//refresh传递值为true，这样就自动调用了refresh方法进行了刷新
    refresh();
  }
}

@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
  synchronized (this.beanFactoryMonitor) {
    if (this.beanFactory == null) {
      throw new IllegalStateException("BeanFactory not initialized or already closed - " +
          "call 'refresh' before accessing beans via the ApplicationContext");
    }
    return this.beanFactory;
  }
}

public void publishEvent(ApplicationEvent event) {
  Assert.notNull(event, "Event must not be null");
  if (logger.isTraceEnabled()) {
    logger.trace("Publishing event in " + getDisplayName() + ": " + event);
  }
  getApplicationEventMulticaster().multicastEvent(event);
  if (this.parent != null) {
    this.parent.publishEvent(event);
  }
}

private ApplicationEventMulticaster getApplicationEventMulticaster() throws IllegalStateException {
  if (this.applicationEventMulticaster == null) {//如果为null则抛异常
    throw new IllegalStateException("ApplicationEventMulticaster not initialized - " +
        "call 'refresh' before multicasting events via the context: " + this);
  }
  return this.applicationEventMulticaster;
}