Spring源码分析（二）拓展篇 - registerBeanPostProcessors(beanFactory)

a、在这一步中主要是做了什么东西？

这一步是为了实例化并且注册所有的beanPostProcessor，为了方便在后期初始化其他bean对象的时候直接使用。
常用的BPP有
1、ApplicationContextAwareProcessor
2、AbstractAutoProxyCreator ——> AspectJAwareAdvisorAutoProxyCreator
3、AutowiredAnnotationBeanPostProcessor
4、CommonAnnotationBeanPostProcessor
5、ApplicationListenerDetector
6、AspectJAwareAdvisorAutoProxyCreator
7、InitDestroyAnnotationBeanPostProcessor（处理@postConstruct,@PreDestroy）

其中在prepareBeanFactory中添加的BPP有ApplicationContextAwareProcessor和ApplicationListenerDetector
在invokeBFPP中添加的BPP有ImportAwareBeanPostProcessor

1、关键代码

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

        // 找到所有实现了BeanPostProcessor接口的类
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        // Register BeanPostProcessorChecker that logs an info message when
        // a bean is created during BeanPostProcessor instantiation, i.e. when
        // a bean is not eligible for getting processed by all BeanPostProcessors.
        // 记录下BeanPostProcessor的目标计数
        // 此处为什么要+1呢，原因非常简单，在此方法的最后会添加一个BeanPostProcessorChecker的类
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        // 添加BeanPostProcessorChecker(主要用于记录信息)到beanFactory中
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

        // Separate between BeanPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        // 定义存放实现了PriorityOrdered接口的BeanPostProcessor集合
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
        // 定义存放spring内部的BeanPostProcessor
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
        // 定义存放实现了Ordered接口的BeanPostProcessor的name集合
        List<String> orderedPostProcessorNames = new ArrayList<>();
        // 定义存放普通的BeanPostProcessor的name集合
        List<String> nonOrderedPostProcessorNames = new ArrayList<>();
        // 遍历beanFactory中存在的BeanPostProcessor的集合postProcessorNames，
        for (String ppName : postProcessorNames) {
            // 如果ppName对应的BeanPostProcessor实例实现了PriorityOrdered接口，则获取到ppName对应的BeanPostProcessor的实例添加到priorityOrderedPostProcessors中
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                // 如果ppName对应的BeanPostProcessor实例也实现了MergedBeanDefinitionPostProcessor接口，那么则将ppName对应的bean实例添加到internalPostProcessors中
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            // 如果ppName对应的BeanPostProcessor实例没有实现PriorityOrdered接口，但是实现了Ordered接口，那么将ppName对应的bean实例添加到orderedPostProcessorNames中
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            } else {
                // 否则将ppName添加到nonOrderedPostProcessorNames中
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // First, register the BeanPostProcessors that implement PriorityOrdered.
        // 首先，对实现了PriorityOrdered接口的BeanPostProcessor实例进行排序操作
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        // 注册实现了PriorityOrdered接口的BeanPostProcessor实例添加到beanFactory中
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // Next, register the BeanPostProcessors that implement Ordered.
        // 注册所有实现Ordered的beanPostProcessor
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
        for (String ppName : orderedPostProcessorNames) {
            // 根据ppName找到对应的BeanPostProcessor实例对象
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            // 将实现了Ordered接口的BeanPostProcessor添加到orderedPostProcessors集合中
            orderedPostProcessors.add(pp);
            // 如果ppName对应的BeanPostProcessor实例也实现了MergedBeanDefinitionPostProcessor接口，那么则将ppName对应的bean实例添加到internalPostProcessors中
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        // 对实现了Ordered接口的BeanPostProcessor进行排序操作
        sortPostProcessors(orderedPostProcessors, beanFactory);
        //  注册实现了Ordered接口的BeanPostProcessor实例添加到beanFactory中
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);

        // Now, register all regular BeanPostProcessors.
        // 创建存放没有实现PriorityOrdered和Ordered接口的BeanPostProcessor的集合
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
        // 遍历集合
        for (String ppName : nonOrderedPostProcessorNames) {
            // 根据ppName找到对应的BeanPostProcessor实例对象
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            // 将没有实现PriorityOrdered和Ordered接口的BeanPostProcessor添加到nonOrderedPostProcessors集合中
            nonOrderedPostProcessors.add(pp);
            // 如果ppName对应的BeanPostProcessor实例也实现了MergedBeanDefinitionPostProcessor接口，那么则将ppName对应的bean实例添加到internalPostProcessors中
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        //  注册没有实现PriorityOrdered和Ordered的BeanPostProcessor实例添加到beanFactory中
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

        // Finally, re-register all internal BeanPostProcessors.
        // 将所有实现了MergedBeanDefinitionPostProcessor类型的BeanPostProcessor进行排序操作
        sortPostProcessors(internalPostProcessors, beanFactory);
        // 注册所有实现了MergedBeanDefinitionPostProcessor类型的BeanPostProcessor到beanFactory中
        registerBeanPostProcessors(beanFactory, internalPostProcessors);

        // Re-register post-processor for detecting inner beans as ApplicationListeners,
        // moving it to the end of the processor chain (for picking up proxies etc).
        // 注册ApplicationListenerDetector到beanFactory中
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }

2、关键流程