1.目的
以前也稍微了解spring的源码，最近在研究研究，记录一下心得。
今天就针对spring中BeanPostProcessor的理解进行加深一下。
2.BeanPostProcessor是什么？
spring中基础对象都是bean! 那么beanPostProcessor也是一个bean，只不过多了一层关系，实现BeanPostProcessor接口。
2.1.beanPostProcessor如何被识别出来的？
在AbstractApplicationContext方法中registerBeanPostProcessors()
代码行数：
版本：spring-core-3.0.0.RELEASE-sources.jar
方法中：AbstractApplicationContext.registerBeanPostProcessors（） 401行
registerBeanPostProcessors(beanFactory);
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
2.2.beanPostProcessor中的方法何时被调用？
在bean初始化的时候，也就是Spring激活bean的init-method方法的前后，会调用BeanPostProcessor的postProcessBeforeInitialization方法和postProcessAfterInitialization。
代码行数：
版本：spring-core-3.0.0.RELEASE-sources.jar
方法中：AbstractAutowireCapableBeanFactory.initializeBean（）
1394
1407
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
3.分析一下BeanPostProcessor的实现类ApplicationContextAwareProcessor
3.1.ApplicationContextAwareProcessor的作用？
如果bean实现ApplicationContextAware的接口，那么就会将applicationContext注入到这个bean中。
3.2.ApplicationContextAwareProcessor实现原理：
1.添加到容器中：在AbstractApplicationContext的refresh方法中的prepareBeanFactory(beanFactory);方法。添加了ApplicationContextAwareProcessor处理器
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
.....
...
..
}
2.调用地方：ApplicationContextAwareProcessor是继承了BeanPostProcessor接口。在bean初始化的时候，也就是Spring激活bean的init-method方法的前后，会调用BeanPostProcessor的postProcessBeforeInitialization方法和postProcessAfterInitialization。
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
3.3.ApplicationContextAware的作用。
通过对ApplicationContextAwareProcessor的分析，我们可以清楚的了解ApplicationContextAware的作用：对当前bean传入对应的Spring上下文。(即得到applicationContext)
3.4.ApplicationContextAware的使用实例。
请点击以下的文章（自己看）
请点击---文章1
3.5.ApplicationContextAwareProcessor的使用实例
请点击---[文章2](https://blog.csdn.net/qq_34310242/article/details/78266590)
4.参考目录
推荐：https://blog.csdn.net/mdq11111/article/details/79050280
