Spring中为什么继承了ApplicationContextAware接口就可以使用ApplicationContext对象？

1、Spring中使用applicationContext对象

public class SpringContextUtil implements ApplicationContextAware
{
    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext)
    {
        applicationContext = applicationContext;
    }

    public static ApplicationContext getApplicationContext()
    {
        return applicationContext;
    }
}

2、为什么继承ApplicationContextAware就可以使用applicationContext对象？

使用后置处理器

3、什么是后置处理器？
      后置处理器主要是对bean进行增强，包括在bean初始化前和初始化后进行增强，如修改bean属性、对bean的方法进行代理等。

public interface BeanPostProcessor {
     // bean初始化前增强
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
// bean初始化后增强
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

4、后置处理器怎样调用setApplicationContext赋值？

内置后置处理器：org.springframework.context.support.ApplicationContextAwareProcessor

class  ApplicationContextAwareProcessor implements BeanPostProcessor 

public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {

        else {
            invokeAwareInterfaces(bean);
        }

        return bean;
    }

private void invokeAwareInterfaces(Object bean) {
        if (bean instanceof Aware) {
            // 对继承于ApplicationContextAware的bean调用setApplicationContext方法进行赋值
            if (bean instanceof ApplicationContextAware) {
                ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
            }
        }
    }

5、参考资料

https://blog.csdn.net/baomw/article/details/84262006