Aware

Aware

容器对 Bean 本身的逻辑基本是无侵入的，所以Bean一般不需要了解容器的状态和直接使用容器；但是有的时候是需要在 Bean 中直接操作 容器,所以需要在 Bean中设定对容器的感知；就要使用 Aware 接口的作用。

当我们的类需要容器提供帮助的时候，就需要告知容器，类能够感知到容器的存在—区别于一般的普通类，需要实现特定类型的 Aware接口。

Aware接口 没有任何方法，只是做标签来使用。所以在 Spring 中起作用的 是继承了 Aware的具体接口；

常见接口如下：

ApplicationContextAware

实现该接口的 Bean 在容器创建这个 Bean 实例的时候，将容器本身的实例作为参数传入，给这个 Bean 实例使用，Bean实例使用成员变量接收后，直接使用这个 ApplicationContext 的实例

public interface ApplicationContextAware extends Aware {

   /**
    * Set the ApplicationContext that this object runs in.
    * Normally this call will be used to initialize the object.
    * <p>Invoked after population of normal bean properties but before an init callback such
    * as {@link org.springframework.beans.factory.InitializingBean#afterPropertiesSet()}
    * or a custom init-method. Invoked after {@link ResourceLoaderAware#setResourceLoader},
    * {@link ApplicationEventPublisherAware#setApplicationEventPublisher} and
    * {@link MessageSourceAware}, if applicable.
    * @param applicationContext the ApplicationContext object to be used by this object
    * @throws ApplicationContextException in case of context initialization errors
    * @throws BeansException if thrown by application context methods
    * @see org.springframework.beans.factory.BeanInitializationException
    */
   void setApplicationContext(ApplicationContext applicationContext) throws BeansException;

}

BeanNameAware

将 Bean的名字传入，供实现了这个接口的 Bean 实例使用

public interface BeanNameAware extends Aware {

   /**
    * Set the name of the bean in the bean factory that created this bean.
    * <p>Invoked after population of normal bean properties but before an
    * init callback such as {@link InitializingBean#afterPropertiesSet()}
    * or a custom init-method.
    * @param name the name of the bean in the factory.
    * Note that this name is the actual bean name used in the factory, which may
    * differ from the originally specified name: in particular for inner bean
    * names, the actual bean name might have been made unique through appending
    * "#..." suffixes. Use the {@link BeanFactoryUtils#originalBeanName(String)}
    * method to extract the original bean name (without suffix), if desired.
    */
   void setBeanName(String name);

}

BeanFactoryAware

获取 当前 BeanFactory 的实例，获取容器的服务

public interface BeanFactoryAware extends Aware {

   /**
    * Callback that supplies the owning factory to a bean instance.
    * <p>Invoked after the population of normal bean properties
    * but before an initialization callback such as
    * {@link InitializingBean#afterPropertiesSet()} or a custom init-method.
    * @param beanFactory owning BeanFactory (never {@code null}).
    * The bean can immediately call methods on the factory.
    * @throws BeansException in case of initialization errors
    * @see BeanInitializationException
    */
   void setBeanFactory(BeanFactory beanFactory) throws BeansException;

}

MessageSourceAware

获取 MessageSource 相关的文本信息

public interface MessageSourceAware extends Aware {

   /**
    * Set the MessageSource that this object runs in.
    * <p>Invoked after population of normal bean properties but before an init
    * callback like InitializingBean's afterPropertiesSet or a custom init-method.
    * Invoked before ApplicationContextAware's setApplicationContext.
    * @param messageSource message source to be used by this object
    */
   void setMessageSource(MessageSource messageSource);

}

ApplicationEventPublisherAware

获取发布器实例，用来发布事件---事件驱动模型

public interface ApplicationEventPublisherAware extends Aware {

   /**
    * Set the ApplicationEventPublisher that this object runs in.
    * <p>Invoked after population of normal bean properties but before an init
    * callback like InitializingBean's afterPropertiesSet or a custom init-method.
    * Invoked before ApplicationContextAware's setApplicationContext.
    * @param applicationEventPublisher event publisher to be used by this object
    */
   void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher);

}

ResourceLoaderAware

获取资源加载器，用于获取外部资源文件

以上具体Aware接口中的 各种 set方法是设置不同的东西，供实现这个接口的 Bean 实例使用，这些 set 方法是 Spring框架会调用的---只要实例实现了相应的接口；告知Spring需要使用什么，然后 Spring会调用set方法进行设置。

注意：实现这些接口的 Bean 必须是容器 管理的 Bean ；这样各种类型的 Aware 才会起作用。

@Controller
public class WelcomeController implements ApplicationContextAware, BeanNameAware {

   private String myName;

   private ApplicationContext myContainer;

   @Autowired
   private WelcomeService welcomeService;

   public void doRequest() {
      welcomeService.sayHello("来自Controller的调用问候");
      System.out.println("我是谁：" + myName);
      System.out.println("我所在的容器：" + myContainer);
      String[] allBeanNames = myContainer.getBeanDefinitionNames();
      for (String beanName : allBeanNames) {
         System.out.println(beanName);
      }
      System.out.println("======================");
   }

   @Override
   public void setBeanName(String name) {
      this.myName = name;
   }

   @Override
   public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
      this.myContainer = applicationContext;
   }
}

输出如下：

我是谁：welcomeController
我所在的容器：org.springframework.context.annotation.AnnotationConfigApplicationContext@1e80bfe8, started on Tue Jun 30 19:51:29 CST 2020
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
entrance
welcomeController
welcomeDao
customizedBeanDefinitionRegistryPostProcessor
customizedBeanPostProcessor
welcomeServiceImpl

user5