001-BeanPostProcessor

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

推荐：https://www.jianshu.com/p/2692bf784976

https://www.jianshu.com/p/a90a3e617ba6