Spring框架你敢写精通，面试官就敢问@Autowired注解的实现原理

 public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
      // Prepare this context for refreshing.
      prepareRefresh();

      // Tell the subclass to refresh the internal bean factory.
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory);

      try {
        // Allows post-processing of the bean factory in context subclasses.
        postProcessBeanFactory(beanFactory);

        // Invoke factory processors registered as beans in the context.
        invokeBeanFactoryPostProcessors(beanFactory);

        // Register bean processors that intercept bean creation.
        // 重点看这里：在这里对AutowiredAnnotationBeanPostProcessor注册
        registerBeanPostProcessors(beanFactory);

        // 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.
        // 重点看这里：对非延迟初始化的单例bean进行初始化
        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();
      }
    }
  }

synchronized (mbd.postProcessingLock) {
  if (!mbd.postProcessed) {
    try {
      applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
    }
    catch (Throwable ex) {
      throw new BeanCreationException(mbd.getResourceDescription(), beanName,
          "Post-processing of merged bean definition failed", ex);
    }
    mbd.postProcessed = true;
  }
}

protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
  for (BeanPostProcessor bp : getBeanPostProcessors()) {
    if (bp instanceof MergedBeanDefinitionPostProcessor) {
      MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
      bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
    }
  }
}