Spring源码之ApplicationContext(六)注册BeanPostProcessor

接下来我们继续探索registerBeanPostProcessors的用法。这里需要注意的是，注册拦截Bean创建的Bean处理器，这里只是注册，真正的调用是在getBean时候。（相关资源可到这里下载：http://pan.baidu.com/s/1sjSo9a9）

1. PostProcessorRegistrationDelegate

在AbstractApplicationContext类中，调用函数registerBeanPostProcessors，而这个函数又调用了类PostProcessorRegistrationDelegate中的registerBeanPostProcessors这个函数。所以我们的重心就是在这里分析了。

public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {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.//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//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));// Separate between BeanPostProcessors that implement PriorityOrdered,// Ordered, and the rest.//使用PtiorityOrdered保证顺序List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();//使用Ordered保证顺序List<String> orderedPostProcessorNames = new ArrayList<String>();//无序BeanPostProcessorList<String> nonOrderedPostProcessorNames = new ArrayList<String>();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);}}// First, register the BeanPostProcessors that implement PriorityOrdered.sortPostProcessors(beanFactory, priorityOrderedPostProcessors);registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);// Next, register the BeanPostProcessors that implement Ordered.List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();for (String ppName : orderedPostProcessorNames) {BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);orderedPostProcessors.add(pp);if (pp instanceof MergedBeanDefinitionPostProcessor) {internalPostProcessors.add(pp);}}sortPostProcessors(beanFactory, orderedPostProcessors);registerBeanPostProcessors(beanFactory, orderedPostProcessors);// Now, register all regular BeanPostProcessors.List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();for (String ppName : nonOrderedPostProcessorNames) {BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);nonOrderedPostProcessors.add(pp);if (pp instanceof MergedBeanDefinitionPostProcessor) {internalPostProcessors.add(pp);}}registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);// Finally, re-register all internal BeanPostProcessors.sortPostProcessors(beanFactory, internalPostProcessors);registerBeanPostProcessors(beanFactory, internalPostProcessors);beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));}

在函数的调用中，可能读者会认为对于internalPostProcessons中存储的后处理器也是MergedBeanDefinitionPostProcessor类型的处理器，在代码中似乎是被重复调用了，其实是不然，我们可以看registerBeanPostProcessor方法的实现。

private static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {for (BeanPostProcessor postProcessor : postProcessors) {beanFactory.addBeanPostProcessor(postProcessor);}}

2. AbstractBeanFactory

我们通过最后的registerBeanPostProcessors的函数并没有得不到我们提出的疑问，别急，我们继续看一下addBeanPostProcessor的函数。分析一个问题的答案就出来了。

public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");this.beanPostProcessors.remove(beanPostProcessor);this.beanPostProcessors.add(beanPostProcessor);if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {this.hasInstantiationAwareBeanPostProcessors = true;}if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {this.hasDestructionAwareBeanPostProcessors = true;}}