ApplicationContextAware的setApplicationContext方法是什么时候执行的

可以肯定的是在从容器中getbean的过程中调用的，简单说下几个主要流程

1. getbean到调用bean后处理器
   getbean的流程参见下图，主要参考标红字体部分
   
   从图中可以看出，最后会调用initializeBeanf方法又会调用applyBeanPostProcessorsBeforeInitialization、applyBeanPostProcessorsAfterInitialization方法，也就是调用bean后处理器。

2. bean后处理器其中就有一个叫ApplicationContextAwareProcessor,其中的处理方法如下代码，就有调用到setApplicationContext方法

   @Override
   @Nullable
   public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
   AccessControlContext acc = null;

       if (System.getSecurityManager() != null &&
               (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
                       bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
                       bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
           acc = this.applicationContext.getBeanFactory().getAccessControlContext();
       }
   if (acc != null) {
       AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
           invokeAwareInterfaces(bean);
           return null;
       }, acc);
   }
   else {
       invokeAwareInterfaces(bean);
   }
   
   return bean;
   }
   
   private void invokeAwareInterfaces(Object bean) {
       if (bean instanceof Aware) {
           if (bean instanceof EnvironmentAware) {
               ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
           }
           if (bean instanceof EmbeddedValueResolverAware) {
               ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
           }
           if (bean instanceof ResourceLoaderAware) {
               ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
           }
           if (bean instanceof ApplicationEventPublisherAware) {
               ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
           }
           if (bean instanceof MessageSourceAware) {
               ((MessageSourceAware) bean).setMessageSource(this.applicationContext);
           }
           if (bean instanceof ApplicationContextAware) {
               ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
           }
       }
   }

3. 你是不是会问ApplicationContextAwareProcessor什么时候放到容器中的，看org.springframework.context.support.AbstractApplicationContext#prepareBeanFactory方法中就放进来了

   protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
   // Tell the internal bean factory to use the context's class loader etc.
   beanFactory.setBeanClassLoader(getClassLoader());
   beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
   beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

       // Configure the bean factory with context callbacks.
       beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
       ······
   }

4.prepareBeanFactory又在org.springframework.context.support.AbstractApplicationContext#refresh方法中被调用，看是不是又回到容器初始化的入口了，整个流程是不是打通了