code: public static Set<String> getLocalizationKeySet() {
          Map<String, Map<String, Object>> msgss = getMessageSet();
          if (null == msgss)
              return new HashSet<String>();
          return msgss.keySet();
      }
docs: 返回当前加载了的本地化字符串的键值
  
  @return 当前都加载了哪些种字符串的 KEY