Spring扩展点之Aware接口族

Java学习录

发布于 2019-09-17 15:01:16

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发布于 2019-09-17 15:01:16

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);

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原始发表：2019-09-16，如有侵权请联系 cloudcommunity@tencent.com 删除

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