Spring启动流程源码之registerBeanPostProcessors

之前的文章已经介绍了refresh中的obtainFreshBeanFactory和invokeBeanFactoryPostProcessors方法，今天来看下refresh中另外一个比较重要的方法registerBeanPostProcessors。

registerBeanPostProcessors的源码在org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors(org.springframework.beans.factory.config.ConfigurableListableBeanFactory, org.springframework.context.support.AbstractApplicationContext)下，具体如下

 public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
        //1、找出所有直接实现BeanPostProcessor接口的类
		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
        
		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        //3、添加BeanPostProcessorChecker(主要用于记录信息)到beanFactory中
		beanFactory.addBeanPostProcessor(new PostProcessorRegistrationDelegate.BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
        
		//3.1、priorityOrderedPostProcessors：继承自PriorityOrdered接口的
		List priorityOrderedPostProcessors = new ArrayList();
		//3.2、internalPostProcessors: 用于存放Spring内部的BeanPostProcessor
        List internalPostProcessors = new ArrayList();
		//3.3、orderedPostProcessorNames: 用于存放实现Ordered接口的
        List orderedPostProcessorNames = new ArrayList();
		//3.4、nonOrderedPostProcessorNames: 用于存放普通的beanName
        List nonOrderedPostProcessorNames = new ArrayList();
		
		
        String[] var8 = postProcessorNames;
        int var9 = postProcessorNames.length;

        String ppName;
        BeanPostProcessor pp;
		//4、遍历postProcessorNames, 将BeanPostProcessors按3.1-3.4定义的变量区分开
        for(int var10 = 0; var10 < var9; ++var10) {
            ppName = var8[var10];
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                pp = (BeanPostProcessor)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);
            }
        }
		//5、对priorityOrderedPostProcessors进行排序
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		//5.1、将priorityOrderedPostProcessors注册到BeanFactory
        registerBeanPostProcessors(beanFactory, (List)priorityOrderedPostProcessors);
        
		List orderedPostProcessors = new ArrayList();
        Iterator var14 = orderedPostProcessorNames.iterator();
		//5.2、遍历orderedPostProcessorNames，获取对应的bean并且添加到orderedPostProcessors/internalPostProcessors
        while(var14.hasNext()) {
            String ppName = (String)var14.next();
            BeanPostProcessor pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
		
        sortPostProcessors(orderedPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, (List)orderedPostProcessors);
        //5.3、重复5.2遍历nonOrderedPostProcessorNames，获取对应的bean并且添加到nonOrderedPostProcessors/internalPostProcessors
		List nonOrderedPostProcessors = new ArrayList();
        Iterator var17 = nonOrderedPostProcessorNames.iterator();

        while(var17.hasNext()) {
            ppName = (String)var17.next();
            pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }

        registerBeanPostProcessors(beanFactory, (List)nonOrderedPostProcessors);
        sortPostProcessors(internalPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, (List)internalPostProcessors);
        //6、注册程序监听器
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }

从上方的源码中可以看出registerBeanPostProcessors的主要功能有以下两种：

找出所有实现BeanPostProcessor接口的类，按照实现PriorityOrdered接口、实现Ordered接口、普通的和实现MergedBeanDefinitionPostProcessor接口的依次进行分类、排序、注册；往beanFactory中添加一个程序监听器。

注意：

        1.由于该方法中有getBean()，因此也会涉及getBean--->doGetBean--->createBean---->doCreateBean等操作；

        2.在registerBeanPostProcessors方法中，只是完成了对实现BeanPostProcessor接口的类的分类、排序和注册，但是不会执行，真正执行的地方在finishBeanFactoryInitialization方法中，具体的请看下篇文章。

看完之后估计大家还会有一个问题，它如何找到所有的BeanPostProcessor? 

之前的文章我们说过在refresh()方法中，会先执行完invokeBeanFactoryPostProcessor()方法，这样所有自定义的BeanPostProcessor类均已经被扫描出并解析成BeanDefinition(扫描和解析又是谁做的呢？ConfigurationClassPostProcessor做的)，存入至BeanFactory的BeanDefinitionMap，所以这儿能通过方法如下一行代码找出所有的BeanPostProcessor，然后通过getBean()全部实例化，最后再将实例化后的对象加入到BeanFactory的beanPostProcessors属性中。