Spring BeanPostProcessor

    /**
     * 实例化并调用已经注入的 BeanPostProcessor
     * 必须在应用中 bean 实例化之前调用
     */
 protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
  PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
 }

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

        // 获取所有的 BeanPostProcessor 的 beanName
        // 这些 beanName 都已经全部加载到容器中去，但是没有实例化
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        // 记录所有的beanProcessor数量
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;

        // 注册 BeanPostProcessorChecker，它主要是用于在 BeanPostProcessor 实例化期间记录日志
        // 当 Spring 中高配置的后置处理器还没有注册就已经开始了 bean 的实例化过程，这个时候便会打印 BeanPostProcessorChecker 中的内容
        beanFactory.addBeanPostProcessor(new PostProcessorRegistrationDelegate.BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

        // PriorityOrdered 保证顺序
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
        // MergedBeanDefinitionPostProcessor
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
        // 使用 Ordered 保证顺序
        List<String> orderedPostProcessorNames = new ArrayList<>();
        // 没有顺序
        List<String> nonOrderedPostProcessorNames = new ArrayList<>();
        for (String ppName : postProcessorNames) {
            // PriorityOrdered
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                // 调用 getBean 获取 bean 实例对象
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            // Ordered
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                // 无序
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // 第一步注册所有实现了 PriorityOrdered 的BeanPostProcessor
        // 先排序
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        // 后注册
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // 第二步注册所有实现了 Ordered 的 BeanPostProcessor
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
        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);

        // 第三步注册所有无序的 BeanPostProcessor
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
        for (String ppName : nonOrderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

        // 最后，注册所有的 MergedBeanDefinitionPostProcessor 类型的 BeanPostProcessor
        sortPostProcessors(internalPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, internalPostProcessors);

        // 加入ApplicationListenerDetector（探测器）
        // 重新注册 BeanPostProcessor 以检测内部 bean，因为 ApplicationListeners 将其移动到处理器链的末尾
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }