本节分析下 refresh()中的 registerBeanPostProcessors(beanFactory);方法
public interface BeanPostProcessor {
/**
* Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
* initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
* or a custom init-method). The bean will already be populated with property values.
* The returned bean instance may be a wrapper around the original.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one;
* if {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
*/
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
/**
* Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
* initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
* or a custom init-method). The bean will already be populated with property values.
* The returned bean instance may be a wrapper around the original.
* <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
* instance and the objects created by the FactoryBean (as of Spring 2.0). The
* post-processor can decide whether to apply to either the FactoryBean or created
* objects or both through corresponding {@code bean instanceof FactoryBean} checks.
* <p>This callback will also be invoked after a short-circuiting triggered by a
* {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
* in contrast to all other BeanPostProcessor callbacks.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one;
* if {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
* @see org.springframework.beans.factory.FactoryBean
*/
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}
BeanPostProcessor的作用是一个 在BeanDefinition实例化成一个真正的对象后，在该对象的初始化前和初始化后做一些工作。它和BeanFactoryPostProcess不同， BeanFactoryPostProcess一般是改变下某个BeanDefinition，而不是真的对象。
跟着代码，发现实际调用的是 PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
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. int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length; beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)); // Separate between BeanPostProcessors that implement PriorityOrdered, // Ordered, and the rest. List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>(); List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>(); List<String> orderedPostProcessorNames = new ArrayList<String>(); List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
其实跟上一节的beanFactoryPostProcessor过程类似，在查找 BeanPostProcessor的Bean 名字时，都是按照 PriorityOrdered， Ordered， 和没有实现这两个接口的普通类的顺序，依次实例化和初始化生成这些bean，并且注册到beanFactory中
AbstractBeanFactory中的方法 addBeanPostProcessor，注意是 先 remove再 add
@Override
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;
}
}
InstantiationAwareBeanPostProcessor 这是一个值得注意的BeanPostProcessor，它的接口定义如下
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor { Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException; boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;//动态代理就是用的这个 PropertyValues postProcessPropertyValues( PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException;//填充属性的方法，比如@AutoWired @Resources @Value }
他的实现类有哪些呢？
1 AnnotationAwareAspectJAutoProxyCreator 动态代理
2 AutowiredAnnotationBeanPostProcessor 解决@AutoWired注解的
3 CommonAnnotationBeanPostProcessor
回到registerBeanPostProcessors方法中 里面有一个特别需要注意的地方
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
如果某一个BeanPostProcessor实现了MergedBeanDefinitionPostProcessor这个接口，把它单独的放到 internalPostProcessors这个list中保存起来，并且在实例化，并注册到了beanFactory之后，最后再做一次把这些MergedBeanDefinitionPostProcessor注册进去。
MergedBeanDefinitionPostProcessor 的作用就是负责把一个Bean的@AutoWired或者@Resource等注解的信息缓存起来留着后来使用
// Finally, re-register all internal BeanPostProcessors. sortPostProcessors(beanFactory, internalPostProcessors); registerBeanPostProcessors(beanFactory, internalPostProcessors);
所以，我们之前说注册时先remove再add，这样就能保证这些 internal BeanPostProcessors肯定是在AbstractBeanFactory中保存所有beanPostProcessor的最后。
MergedBeanDefinitionPostProcessor的实现类有哪些呢？
比较常见的有两个 AutowiredAnnotationBeanPostProcessor， CommonAnnotationBeanPostProcessor
AutowiredAnnotationBeanPostProcessor就是用来处理一个spring bean中autowired注解的，而 CommonAnnotationBeanPostProcessor是处理resource注解的。resource注解是java的不是spring的。
下一节，会分析beanFactory实例化的代码，就能够看到beanPostProcessor是怎么使用的了。
总结
BeanPostProcesssor最值得记忆的两个实现类
1 InstantiationAwareBeanPostProcessor 既能处理属性值填充，也能处理动态代理
2 MergedBeanDefinitionPostProcessor 专门收集自动注入等注解，并缓存起来