Spring的Aware接口有什么用？

爱被打了一巴掌 2023-09-29 14:46 8阅读 0赞

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);
    		}
    	}

将相应的对象set进自定义对象

然后自定义对象就可以使用这些容器对象的能力了

spring内部也经常可见这种用法

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[4a6f4b4ba77c45889b6bacd31daa9f1b.png]: https://img-blog.csdnimg.cn/4a6f4b4ba77c45889b6bacd31daa9f1b.png