spring源码-4.注册bean的后处理器

执行完beanFactory的后处理器后，在实例化beanDefinition前，我们需要将bean的后处理器注册到容器中，这样才能在实例化beanDefinition的时候去执行这些后处理器。
首先我们来看一下这个方法的入口（AbstractApplicationContext）：

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}

进入registerBeanPostProcessors方法：

public static void registerBeanPostProcessors(
			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
    //获取所有beanDefinition的类型为BeanPostProcessor的name
	String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

	//在prepareBeanFactory方法中，已经添加了三个，所以计算count的时候需要加上之前的和下面这个新增的
	int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
	beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    //用于记录实现priorityOrdered接口的后处理器
	List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
	//用于记录内置的后处理器
	List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
	//用于记录实现ordered接口的后处理器
	List<String> orderedPostProcessorNames = new ArrayList<>();
	//用于记录剩余的后处理器
	List<String> nonOrderedPostProcessorNames = new ArrayList<>();
	//遍历之前通过type获取到的bean的后处理器，并进行分类
	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);
		}
	}

    /**
    * 下面分三步将这些后处理器进行注册，这里有一个概念需要解释一下，MergedBeanDefinitionPostProcessor是
    * BeanPostProcessor的子接口，如果实现了MergedBeanDefinitionPostProcessor，则认为是一个内置的后处理器。
    */
	//首先，将priorityOrdered类的进行排序，并注册
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

	//首先，将ordered类的进行排序，并注册
	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);

	//最后，将剩余的没有排序的后处理器进行注册
	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);

	//最后，对内置的后处理器进行排序，并注册
	sortPostProcessors(internalPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, internalPostProcessors);

	//到这里，所有的bean的后处理器都已加入到beanFactory中了，这里再添加一个ApplicationListenerDetector后处理器
	beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}