参考源

https://www.bilibili.com/video/BV1tR4y1F75R?spm_id_from=333.337.search-card.all.click

https://www.bilibili.com/video/BV12Z4y197MU?spm_id_from=333.999.0.0

《Spring源码深度解析（第2版）》

版本

本文章基于 Spring 5.3.15

Spring IOC 的核心是 AbstractApplicationContext 的 refresh 方法。

其中一共有 13 个主要方法，这里分析第 6 个：registerBeanPostProcessors。

1 AbstractApplicationContext

1-1 注册 Bean 增强器

registerBeanPostProcessors(beanFactory)

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {

    // 注册 Bean 增强器

    PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);

}

1-2 注册 Bean 增强器

PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this)

2 PostProcessorRegistrationDelegate

public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

   String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

   /**

    * BeanPostProcessorChecker 是一个普通的信息打印，可能会有些情况

    * 当 Spring 的配置中的后处理器还没有被注册就已经开始了 bean 的初始化时

    * 便会打印出 BeanPostProcessorChecker 中设定的信息

    */

   int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;

   beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

   // 使用 PriorityOrdered 保证顺序

   List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();

   List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();

   // 使用 Ordered 保证顺序

   List<String> orderedPostProcessorNames = new ArrayList<>();

   // 无序 BeanPostProcessor

   List<String> nonOrderedPostProcessorNames = new ArrayList<>();

   for (String ppName : postProcessorNames) {

      if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {

         BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);

         priorityOrderedPostProcessors.add(pp);

         if (pp instanceof MergedBeanDefinitionPostProcessor) {

            internalPostProcessors.add(pp);

         }

      } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {

         orderedPostProcessorNames.add(ppName);

      } else {

         nonOrderedPostProcessorNames.add(ppName);

      }

   }

   // 第 1 步，排序增强器。注册所有实现 PriorityOrdered 的 BeanPostProcessor

   sortPostProcessors(priorityOrderedPostProcessors, beanFactory);

   // 注册 Bean 增强器

   registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

   // 第 2 步，注册所有实现 Ordered 的 BeanPostProcessor

   List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());

   for (String ppName : orderedPostProcessorNames) {

      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);

      orderedPostProcessors.add(pp);

      if (pp instanceof MergedBeanDefinitionPostProcessor) {

         internalPostProcessors.add(pp);

      }

   }

   sortPostProcessors(orderedPostProcessors, beanFactory);

   registerBeanPostProcessors(beanFactory, orderedPostProcessors);

   // 第 3 步，注册所有无序的 BeanPostProcessor

   List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());

   for (String ppName : nonOrderedPostProcessorNames) {

      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);

      nonOrderedPostProcessors.add(pp);

      if (pp instanceof MergedBeanDefinitionPostProcessor) {

         internalPostProcessors.add(pp);

      }

   }

   registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

   /**

    * 第 4 步，注册所有 MergedBeanDefinitionPostProcessor 类型的 BeanPostProcessor，并非重复注册

    * 在 beanFactory.addBeanPostProcessor 中会先移除已经存在的 BeanPostProcessor

    */

   sortPostProcessors(internalPostProcessors, beanFactory);

   registerBeanPostProcessors(beanFactory, internalPostProcessors);

   // 添加 ApplicationListener 探测器

   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));

}

2-1 排序增强器

sortPostProcessors(priorityOrderedPostProcessors, beanFactory)

private static void sortPostProcessors(List<?> postProcessors, ConfigurableListableBeanFactory beanFactory) {

   if (postProcessors.size() <= 1) {

      return;

   }

   Comparator<Object> comparatorToUse = null;

   if (beanFactory instanceof DefaultListableBeanFactory) {

      comparatorToUse = ((DefaultListableBeanFactory) beanFactory).getDependencyComparator();

   }

   if (comparatorToUse == null) {

      comparatorToUse = OrderComparator.INSTANCE;

   }

   postProcessors.sort(comparatorToUse);

}

2-2 注册 Bean 增强器

registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors)

private static void registerBeanPostProcessors(

      ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {

   if (beanFactory instanceof AbstractBeanFactory) {

      // Bulk addition is more efficient against our CopyOnWriteArrayList there

      ((AbstractBeanFactory) beanFactory).addBeanPostProcessors(postProcessors);

   }

   else {

      for (BeanPostProcessor postProcessor : postProcessors) {

         beanFactory.addBeanPostProcessor(postProcessor);

      }

   }

}