BeanPostProcessor处理的是bean对象，也就是说已经完成了实例化。通过过该方法也只可以知道，我们可以定制bean的数据，例如重置值等。
public interface BeanPostProcessor {
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
}
基于该接口还拓展了其他的接口，例如InstantiationAwareBeanPostProcessor是在实例化前后处理，或者重置属性值。
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
return null;
}
default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
return true;
}
default PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
return pvs;
}
}
下面看下是哪里处理的：
refresh方法的registerBeanPostProcessors。注意，在执行这个方法时，所有的beanDefinition已经完成了。这个方法主要时实例化处理器，并放入到处理器集合中。
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
// 得到所有BeanPostProcessor类型的。
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<>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 区分出PriorityOrdered接口，Ordered接口，普通类型
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);
}
}
// 排序，依旧是在order值排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 添加到处理器集合中。
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// 实例化Ordered接口的.
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);
}
}
// 排序，并放入到处理器集合
sortPostProcessors(orderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// 实例化普通类型的。
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);
}
}
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
// Finally, re-register all internal BeanPostProcessors.
sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);
// Re-register post-processor for detecting inner beans as ApplicationListeners,
// moving it to the end of the processor chain (for picking up proxies etc).
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
这个和beanFactory处理器的逻辑一致。注意：这里只是实例化。真正调用的时候时在实例化bean的过程中。
这里有个需要注意的地方：
如果我们自定义bean处理器，其中依赖了以他的bean。实例化处理器之前要先实例其他的bean,可是如果有的bean处理器还有实例化完成，那么实例的bean就会应用不到处理器。
举个例子：定义处理器实现了PriorityOrdered，并且order最小。那么他就会最先实例化。如果依赖bean_A，beanA中用依赖出入了b,c使用了注解@autowired.那么将不生效。因为，此时，注入的bean处理器还有没有实例化呢，对Bean_A应用不到。所以，bean处理器尽量不要依赖自定义的bean.
在bean处理器实例化前，添加了一个处理器：
// 当前处理器的个数
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
这也是个bean处理器
private static final class BeanPostProcessorChecker implements BeanPostProcessor {
public Object postProcessAfterInitialization(Object bean, String beanName) {
// 对于自定义的bean,如果bean处理器还没有全部实例化，那么会提醒你：
// 这个bean不能被所有的处理器处理。
if (!(bean instanceof BeanPostProcessor) && !isInfrastructureBean(beanName) &&
this.beanFactory.getBeanPostProcessorCount() < this.beanPostProcessorTargetCount) {
if (logger.isInfoEnabled()) {
logger.info("Bean '" + beanName + "' of type [" + bean.getClass().getName() +
"] is not eligible for getting processed by all BeanPostProcessors " +
"(for example: not eligible for auto-proxying)");
}
}
return bean;
}
