处理完BeanFactoryPostProcessor后，接下来要处理的就是BeanPostProcessor，在refresh()方法中，调用 registerBeanPostProcessors 方法处理：
// Register bean processors that intercept bean creation.
// 注册bean处理器，这里只是注册功能，真正调用的是getBean方法
registerBeanPostProcessors(beanFactory);
BeanPostProcessors 的处理逻辑和 BeanFactoryPostProcessor 的处理逻辑类似，通过 beanFactory.getBeanNamesForType方法拿到 beanFactory 中的实现了BeanPostProcessor接口的类，然后按照 PriorityOrdered、Ordered、nonOrdered的分类来处理。在registerBeanPostProcessors方法中只是注册功能，真正调用的是getBean方法。
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
// 找到所有实现了BeanPostProcessor接口的类
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.
// 记录下BeanPostProcessor的目标计数
// 此处为什么要+1呢，原因非常简单，在此方法的最后会添加一个BeanPostProcessorChecker的类
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
// 添加BeanPostProcessorChecker(主要用于记录信息)到beanFactory中
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
// Separate between BeanPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
// 定义存放实现了PriorityOrdered接口的BeanPostProcessor集合
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// 定义存放spring内部的BeanPostProcessor
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
// 定义存放实现了Ordered接口的BeanPostProcessor的name集合
List<String> orderedPostProcessorNames = new ArrayList<>();
// 定义存放普通的BeanPostProcessor的name集合
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 遍历beanFactory中存在的BeanPostProcessor的集合postProcessorNames，
for (String ppName : postProcessorNames) {
// 如果ppName对应的BeanPostProcessor实例实现了PriorityOrdered接口，则获取到ppName对应的BeanPostProcessor的实例添加到priorityOrderedPostProcessors中
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
// 如果ppName对应的BeanPostProcessor实例也实现了MergedBeanDefinitionPostProcessor接口，那么则将ppName对应的bean实例添加到internalPostProcessors中
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 如果ppName对应的BeanPostProcessor实例没有实现PriorityOrdered接口，但是实现了Ordered接口，那么将ppName对应的bean实例添加到orderedPostProcessorNames中
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
} else {
// 否则将ppName添加到nonOrderedPostProcessorNames中
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
// 首先，对实现了PriorityOrdered接口的BeanPostProcessor实例进行排序操作
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 注册实现了PriorityOrdered接口的BeanPostProcessor实例添加到beanFactory中
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
// 注册所有实现Ordered的beanPostProcessor
List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String ppName : orderedPostProcessorNames) {
// 根据ppName找到对应的BeanPostProcessor实例对象
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
// 将实现了Ordered接口的BeanPostProcessor添加到orderedPostProcessors集合中
orderedPostProcessors.add(pp);
// 如果ppName对应的BeanPostProcessor实例也实现了MergedBeanDefinitionPostProcessor接口，那么则将ppName对应的bean实例添加到internalPostProcessors中
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 对实现了Ordered接口的BeanPostProcessor进行排序操作
sortPostProcessors(orderedPostProcessors, beanFactory);
// 注册实现了Ordered接口的BeanPostProcessor实例添加到beanFactory中
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// Now, register all regular BeanPostProcessors.
// 创建存放没有实现PriorityOrdered和Ordered接口的BeanPostProcessor的集合
List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
// 遍历集合
for (String ppName : nonOrderedPostProcessorNames) {
// 根据ppName找到对应的BeanPostProcessor实例对象
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
// 将没有实现PriorityOrdered和Ordered接口的BeanPostProcessor添加到nonOrderedPostProcessors集合中
nonOrderedPostProcessors.add(pp);
// 如果ppName对应的BeanPostProcessor实例也实现了MergedBeanDefinitionPostProcessor接口，那么则将ppName对应的bean实例添加到internalPostProcessors中
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 注册没有实现PriorityOrdered和Ordered的BeanPostProcessor实例添加到beanFactory中
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
// Finally, re-register all internal BeanPostProcessors.
// 将所有实现了MergedBeanDefinitionPostProcessor类型的BeanPostProcessor进行排序操作
sortPostProcessors(internalPostProcessors, beanFactory);
// 注册所有实现了MergedBeanDefinitionPostProcessor类型的BeanPostProcessor到beanFactory中
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).
// 注册ApplicationListenerDetector到beanFactory中
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
BeanPostProcessor 主要接口有两个方法：
初始化方法调用前要进行的处理逻辑
@Nullable
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
初始化方法调用后要进行的处理逻辑
@Nullable
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
在registerBeanPostProcessors方法中手动添加了一个 BeanPostProcessor，BeanPostProcessorChecker的作用主要用于记录信息
// 添加BeanPostProcessorChecker(主要用于记录信息)到beanFactory中
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
我们可以看一下BeanPostProcessorChecker的postProcessAfterInitialization方法，主要就是记录了一下日志信息：
/**
* 后置处理器的after方法，用来判断哪些是不需要检测的bean
* @param bean the new bean instance
* @param beanName the name of the bean
* @return
*/
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
// 如果bean不是BeanPostProcessor实例 && beanName 不是 完全内部使用 && beanFactory当前注册的BeanPostProcessor
// 数量小于 BeanPostProcessor目标数量
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)");
}
}
// 返回bean
return bean;
}
其中有一个 isInfrastructureBean 方法的判断，是用来判断 beanName 是否是完全内部使用，在 BeanDefinition中定义了bean的角色类型：
/**
* 用户自定义bean的角色类型
*
* Role hint indicating that a {@code BeanDefinition} is a major part
* of the application. Typically corresponds to a user-defined bean.
*/
int ROLE_APPLICATION = 0;
/**
* 某些复杂的配置类
*
* Role hint indicating that a {@code BeanDefinition} is a supporting
* part of some larger configuration, typically an outer
* {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
* {@code SUPPORT} beans are considered important enough to be aware
* of when looking more closely at a particular
* {@link org.springframework.beans.factory.parsing.ComponentDefinition},
* but not when looking at the overall configuration of an application.
*/
int ROLE_SUPPORT = 1;
/**
* spring内部使用的bean角色
*
* Role hint indicating that a {@code BeanDefinition} is providing an
* entirely background role and has no relevance to the end-user. This hint is
* used when registering beans that are completely part of the internal workings
* of a {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
*/
int ROLE_INFRASTRUCTURE = 2;
看看 BeanPostProcessor 的比较关键的几个子接口：
- DestructionAwareBeanPostProcessor
postProcessBeforeDestruction在bean被销毁前调用，在BeanFactory的注解中，说明bean的生命周期的时候有提到：
* <p>On shutdown of a bean factory, the following lifecycle methods apply:
* <ol>
* <li>{@code postProcessBeforeDestruction} methods of DestructionAwareBeanPostProcessors
* <li>DisposableBean's {@code destroy}
* <li>a custom destroy-method definition
- MergedBeanDefinitionPostProcessor
/**
*spring通过此方法找出所有需要注入的字段，同时做缓存
*
* Post-process the given merged bean definition for the specified bean.
* @param beanDefinition the merged bean definition for the bean
* @param beanType the actual type of the managed bean instance
* @param beanName the name of the bean
* @see AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors
*/
void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName);
- SmartInstantiationAwareBeanPostProcessor
/**
* 预测bean的类型，主要是在bean还没有创建前我们需要获取bean的类型
*
* Predict the type of the bean to be eventually returned from this
* processor's {@link #postProcessBeforeInstantiation} callback.
* <p>The default implementation returns {@code null}.
* @param beanClass the raw class of the bean
* @param beanName the name of the bean
* @return the type of the bean, or {@code null} if not predictable
* @throws org.springframework.beans.BeansException in case of errors
*/
@Nullable
default Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException {
return null;
}
/**
* 完成对构造函数的解析和推断
*
* Determine the candidate constructors to use for the given bean.
* <p>The default implementation returns {@code null}.
* @param beanClass the raw class of the bean (never {@code null})
* @param beanName the name of the bean
* @return the candidate constructors, or {@code null} if none specified
* @throws org.springframework.beans.BeansException in case of errors
*/
@Nullable
default Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName)
throws BeansException {
return null;
}
/**
* 解决循环依赖问题，通过此方法提前暴露一个合格的对象
*
* Obtain a reference for early access to the specified bean,
* typically for the purpose of resolving a circular reference.
* <p>This callback gives post-processors a chance to expose a wrapper
* early - that is, before the target bean instance is fully initialized.
* The exposed object should be equivalent to the what
* {@link #postProcessBeforeInitialization} / {@link #postProcessAfterInitialization}
* would expose otherwise. Note that the object returned by this method will
* be used as bean reference unless the post-processor returns a different
* wrapper from said post-process callbacks. In other words: Those post-process
* callbacks may either eventually expose the same reference or alternatively
* return the raw bean instance from those subsequent callbacks (if the wrapper
* for the affected bean has been built for a call to this method already,
* it will be exposes as final bean reference by default).
* <p>The default implementation returns the given {@code bean} as-is.
* @param bean the raw bean instance
* @param beanName the name of the bean
* @return the object to expose as bean reference
* (typically with the passed-in bean instance as default)
* @throws org.springframework.beans.BeansException in case of errors
*/
default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
return bean;
}
其中的 getEarlyBeanReference 方法就是用来解决循环依赖问题的。
