code: public static void AssertLegalCosFolderPath(String cosFolderPath) throws ParamException {
          if (cosFolderPath == null || !cosFolderPath.startsWith("/")
                  || !cosFolderPath.endsWith("/")) {
              throw new ParamException(
                      cosFolderPath + " is not cos folder path! Tips: make sure ends with /");
          }
          AssertNotContainIllegalLetter(cosFolderPath);
      }
docs: 判断用户指定的cos目录路径是否合法有效, 即必须以/结尾
  
  @param cosFolderPath cos目录路径
  @throws ParamException