code: public static int getUnReadCount(final Long _userId)
      {
          int ret = 0;
          if (MessageStatusHolder.CACHE.userID2UnRead.containsKey(_userId)) {
              ret = MessageStatusHolder.CACHE.userID2UnRead.get(_userId);
          }
          return ret;
      }
docs: Count of unread messages.
  @param _userId  user id the count is wanted for
  @return count of unread messages