Spring扩展点之Aware接口族-蒲公英云

Spring扩展点之Aware接口族

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

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);