Spring源码：initMessageSource源码解析

Spring源码：initMessageSource源码解析

针对于国际化问题的MessageSource

/**
* Initialize the MessageSource.
* Use parent's if none defined in this context.
*/
protected void initMessageSource() {
   //获取Bean工厂，一般是DefaultListBeanFactory
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   //首先判断是否已有xml文件定义了id为messageSource的bean对象
   if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
      //如果有，则从Bean工厂得到这个bean对象
      this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
      // Make MessageSource aware of parent MessageSource.
      //当父类Bean工厂不为空，并且这个bean对象是HierarchicalMessageSource类型
      if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
         //为HierarchicalMessageSource的实现类
         HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
         //设置父类MessageSource，此处设置内部的parent messageSource
         if (hms.getParentMessageSource() == null) {
            // Only set parent context as parent MessageSource if no parent MessageSource
            // registered already.
            hms.setParentMessageSource(getInternalParentMessageSource());
         }
      }
      if (logger.isTraceEnabled()) {
         logger.trace("Using MessageSource [" + this.messageSource + "]");
      }
   }
   else {
      // Use empty MessageSource to be able to accept getMessage calls.
      //如果没有xml文件定义信息源对象，新建DelegatingMessageSource类作为messageSource的Bean
      //因为DelegatingMessageSource类实现了HierarchicalMessageSource接口，而这个接口继承了MessageSource这个类
      //因此实现了这个接口的类，都是MessageSource的子类，因此DelegatingMessageSource也是一个MessageSource
      DelegatingMessageSource dms = new DelegatingMessageSource();
      //给这个DelegatingMessageSource添加父类消息源
      dms.setParentMessageSource(getInternalParentMessageSource());
      this.messageSource = dms;
      //将这个messageSource实例注册到Bean工厂中
      beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
      if (logger.isTraceEnabled()) {
         logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");
      }
   }
}