注：本系列源码分析基于spring 5.2.2.RELEASE，本文的启动流程针对于
annotation注解方式，gitee仓库链接：gitee.com/funcy/sprin….
接上文，我们继续分析。
6. 注册 BeanPostProcessor: registerBeanPostProcessors(beanFactory)
在正式分析前，需要明确两个概念：
BeanFactoryPostProcessor，被称为BeanFactory的后置处理器，可以对BeanFactory进行一些操作；BeanPostProcessor，被称为Bean的后置处理器，可以对Bean进行一些操作。
不要将本文的BeanPostProcessor与前面的BeanFactoryPostProcessor弄混了。
本文主要是对BeanPostProcessor的register操作(registerBeanPostProcessors(beanFactory))，即将BeanPostProcessor注册到 BeanFactory 中，那么调用是在什么时候呢？既然是对Bean 的操作，当然是有了bean之后再运行了。
BeanPostProcessor也是spring中一个重要组件，关于该组件的详细分析，可以参考spring组件之BeanPostProcessors
废话不多说，直接上代码，同样地，对不重要的方法我们只给出调用链：
|-AbstractApplicationContext#refresh
|-AbstractApplicationContext#registerBeanPostProcessors
|-PostProcessorRegistrationDelegate
#registerBeanPostProcessors(ConfigurableListableBeanFactory, AbstractApplicationContext)
最终调用到了PostProcessorRegistrationDelegate#registerBeanPostProcessors，代码如下：
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
// 获取spring中所有的 BeanPostProcessor，这里仅有一个bean:
// org.springframework.context.annotation.internalAutowiredAnnotationProcessor，
// 即 AutowiredAnnotationBeanPostProcessor
String[] postProcessorNames = beanFactory
.getBeanNamesForType(BeanPostProcessor.class, true, false);
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount()
+ 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(
new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 先获取实现了PriorityOrdered的BeanPostProcessor
// 再获取实现了Ordered的BeanPostProcessor
// 最后再获取不满足以上条件的BeanPostProcessor
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);
}
}
// 处理priorityOrderedPostProcessor：排序，然后添加到beanFactory中
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
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);
}
}
// 处理orderedPostProcessor：排序，然后添加到beanFactory中
sortPostProcessors(orderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
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);
}
}
// 处理余下的BeanPostProcessor：排序，然后添加到beanFactory中
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
// 处理internalPostProcessor：排序，然后添加到beanFactory中
// AutowiredAnnotationBeanPostProcessor实现了MergedBeanDefinitionPostProcessor，
// 因此这里会再次注册
sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
这块代码主要是对BeanFactoryPostProcessor进行注册操作，步骤如下：
- 将实现了
PriorityOrdered的BeanPostProcessor注册到beanFactory中； - 将实现了
Ordered的BeanPostProcessor注册到beanFactory中； - 将不满足上述两个条件的
BeanPostProcessor注册到beanFactory中； - 将所有实现了
MergedBeanDefinitionPostProcessor的BeanPostProcessor再次注册到beanFactory中。
事实上，对demo01而言，这里注册的bean只有一个：AutowiredAnnotationBeanPostProcessor，它同时实现了MergedBeanDefinitionPostProcessor与PriorityOrdered，因此会注册两次。
尽管注册了多次AutowiredAnnotationBeanPostProcessor，但最终只会存在一个，让我们进入registerBeanPostProcessors看看spring是如何注册的，一路跟下去，代码到了AbstractBeanFactory#addBeanPostProcessor:
AbstractBeanFactory#addBeanPostProcessor
private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
@Override
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
// 先进行移除，因此多次注册beanPostProcessors也只存在一个
this.beanPostProcessors.remove(beanPostProcessor);
if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
this.hasInstantiationAwareBeanPostProcessors = true;
}
if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
this.hasDestructionAwareBeanPostProcessors = true;
}
this.beanPostProcessors.add(beanPostProcessor);
}
可以看到，所谓的注册到BeanFactory，其实就是把beanPostProcessor加入到BeanFactory的beanPostProcessors中。
本文仅绍了beanPostProcessor的注册，关于beanPostProcessor的调用，后续的分析再提到，本文的分析就先到这里吧！
本文原文链接：my.oschina.net/funcy/blog/… ，限于作者个人水平，文中难免有错误之处，欢迎指正！原创不易，商业转载请联系作者获得授权，非商业转载请注明出处。
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