Spring扩展点之Aware接口族

淡淡的烟草味﹌ 2024-04-19 10:07 100阅读 0赞

Spring中提供了各种Aware接口，方便从上下文中获取当前的运行环境，比较常见的几个子接口有：BeanFactoryAware,BeanNameAware,ApplicationContextAware,EnvironmentAware，BeanClassLoaderAware等

这些Aware的作用都可以从命名得知

#### **`Aware`的处理** ####

其中`BeanNameAware`、`BeanClassLoaderAware`和`BeanFactoryAware`这三个是直接在bean的初始化之前就处理了的，具体代码在`AbstractAutowireCapableBeanFactory.initializeBean`方法中：

protected Object initializeBean(String beanName, Object bean, RootBeanDefinition mbd) {	
        // 判断对象实现的接口类型，处理特定的三种接口类型：BeanNameAware、BeanClassLoaderAware和BeanFactoryAware。	
        if (bean instanceof BeanNameAware) {	
            ((BeanNameAware) bean).setBeanName(beanName);	
        }	
     	
        if (bean instanceof BeanClassLoaderAware) {	
            ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());	
        }	
     	
        if (bean instanceof BeanFactoryAware) {	
            ((BeanFactoryAware) bean).setBeanFactory(this);	
        }	
        // 开始Bean初始化前处理、初始化、初始化后处理	
        Object wrappedBean = bean;	
        if (mbd == null || !mbd.isSynthetic()) {	
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);	
        }	
     	
        try {	
            invokeInitMethods(beanName, wrappedBean, mbd);	
        }	
        catch (Throwable ex) {	
            throw new BeanCreationException(	
                    (mbd != null ? mbd.getResourceDescription() : null),	
                    beanName, "Invocation of init method failed", ex);	
        }	
     	
        if (mbd == null || !mbd.isSynthetic()) {	
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);	
        }	
        return wrappedBean;	
    }

除了这三种之外的那些Aware接口的实现就不太一样了，它们都是利用`BeanPostProcessor`接口完成的，关于`BeanPostProcessor`接口的原理可以这篇文章：[Spring扩展点之BeanPostProcessor][Spring_BeanPostProcessor]

如`ApplicationContextAware`就是利用`ApplicationContextAwareProcessor`实现的：

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((PrivilegedAction<Object>) () -> {	
            //具体实现	
            invokeAwareInterfaces(bean);	
            return null;	
          }, acc);	
        }	
        else {	
                  //具体实现	
          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);	
          }	
        }	
      }

而`ApplicationContextAwareProcessor`的注册奥秘在`AbstractApplicationContext.prepareBeanFactory`方法中：

beanFactory.setBeanClassLoader(getClassLoader());	
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));	
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); 	
    beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);	
    beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);	
    beanFactory.ignoreDependencyInterface(MessageSourceAware.class);	
    beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

[Spring_BeanPostProcessor]: https://mp.weixin.qq.com/s?__biz=MzU5MDgzOTYzMw==&mid=2247484673&idx=1&sn=8013d8b74d36c74f034247436d51c8ea&scene=21#wechat_redirect