apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/util/ConfigFileUtils.java/ConfigFileUtils/checkFormat
class ConfigFileUtils:  static void checkFormat(final String originalFilename) {
    final List<String> fileNameSplit = Splitter.on(".").splitToList(originalFilename);
    if (fileNameSplit.size() <= 1) {
      throw new BadRequestException("The file format is invalid.");
    }

    for (String s : fileNameSplit) {
      if (StringUtils.isEmpty(s)) {
        throw new BadRequestException("The file format is invalid.");
      }
    }
  }