Bean对IOC容器的感知（aware）

绝地灬酷狼 2022-05-09 10:06 60阅读 0赞

> 在某些情况我们需要对容器中的某些状态需要了解，所以Spring提供了相关的接口，通过特定的aware接口来完成。接口有：
> 
>  *  1）BeanNameAware。可以在bean中得到它在IOC容器中的Bean的实例名字
>  *  2）BeanFactoryAware。可以再Bean中得到Bean所有的Ioc容器，从而直接在Bean中使用IOC容器的服务
>  *  3）ApplicationContextAware。可以在Bean中获取到Bean所有的应用上下文，从而直接在bean中使用应用上下文的服务
>  *  4）MessageSourceAware。在bean中可以得到消息源
>  *  5）ApplicationEventPublisherAware,在bean中可以得到应用上下文的事件发布器，从而可以在bean中发布应用上下文的事件
>  *  6）ResourceLoaderAware，在bean中可以得到ResourceLoader，从而在Bean中使用ResourceLoader加载外部对应的resource资源

具体使用方法：直接实现这个接口，添加set方法即可。

源码实现通过一个的xxxxProcessor（实现了BeanPostProcessor接口）的postProcessBeforeInitialization方法中对aware接口进行注入。例如ApplicationContextAwareProcessor源码：

class ApplicationContextAwareProcessor implements BeanPostProcessor {
        private final ConfigurableApplicationContext applicationContext;
        private final StringValueResolver embeddedValueResolver;
    
        public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
            this.applicationContext = applicationContext;
            this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());
        }
    
        public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
            AccessControlContext acc = null;
            if (System.getSecurityManager() != null && (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware || bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware || bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
                acc = this.applicationContext.getBeanFactory().getAccessControlContext();
            }
    
            if (acc != null) {
                AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    public Object run() {
                        ApplicationContextAwareProcessor.this.invokeAwareInterfaces(bean);
                        return null;
                    }
                }, acc);
            } else {
                this.invokeAwareInterfaces(bean);
            }
    
            return bean;
        }
    
        private void invokeAwareInterfaces(Object bean) {
            if (bean instanceof Aware) {
                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 ApplicationContextAware) {
                    ((ApplicationContextAware)bean).setApplicationContext(this.applicationContext);
                }
            }
    
        }
    
        public Object postProcessAfterInitialization(Object bean, String beanName) {
            return bean;
        }
    }