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BeanPostProcessor
List<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;
}
}