Spring的Aware接口有什么用？-CFANZ编程社区

ioc容器里面的对象分两种，一种是用户自定义对象，一种是容器对象

Aware 接口可以理解为用来获取某些容器对象的方法

获取容器对象肯定是为了想利用容器对象的能力/服务

通过实现某种类型的Aware 来将自定义对象与容器"攀上亲"

例如一个普通的Bean对象，需要用到BeanFactory，可以这样做

@Component
public class MyAware implements BeanFactoryAware {


  BeanFactory beanFactory;

  @Override
  public void setBeanFactory(BeanFactory beanFactory) throws BeansException {

    this.beanFactory = beanFactory;
  }
}

实现BeanFactoryAware，重写setBeanFactory方法即可

Spring是怎么做到的呢？

其实是在初始化自定义类的时候，会调动ApplicationContextAwareProcessor类中的postProcessBeforeInitialization方法

@Override
  @Nullable
  public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
        bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
        bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware ||
        bean instanceof ApplicationStartupAware)) {
      return bean;
    }

    invokeAwareInterfaces(bean);
    return bean;
  }

这个方法会判断当前bean是否是EnvironmentAware、EmbeddedValueResolverAware、ResourceLoaderAware、ApplicationEventPublisherAware、MessageSourceAware、ApplicationContextAware、ApplicationStartupAware中的任意一个

如果是则执行invokeAwareInterfaces方法进行相应的处理

private void invokeAwareInterfaces(Object bean) {
    if (bean instanceof EnvironmentAware) {
      ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
    }
    if (bean instanceof EmbeddedValueResolverAware) {
      ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
    }
    if (bean instanceof ResourceLoaderAware) {
      ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
    }
    if (bean instanceof ApplicationEventPublisherAware) {
      ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
    }
    if (bean instanceof MessageSourceAware) {
      ((MessageSourceAware) bean).setMessageSource(this.applicationContext);
    }
    if (bean instanceof ApplicationStartupAware) {
      ((ApplicationStartupAware) bean).setApplicationStartup(this.applicationContext.getApplicationStartup());
    }
    if (bean instanceof ApplicationContextAware) {
      ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
    }
  }