code: protected EntityImporter buildEntityImporter(String upload, Class<?> clazz) {
      try {
        UploadedFile file = get(upload, UploadedFile.class);
        if (null == file) {
          logger.error("cannot get upload file {}.", upload);
          return null;
        }
        String fileName = get(upload + "FileName");
        InputStream is = new FileInputStream((File) file.getContent());
        String formatName = Strings.capitalize(Strings.substringAfterLast(fileName, "."));
        Option<TransferFormat> format = Enums.get(TransferFormat.class, formatName);
        return (format.isDefined()) ? ImporterFactory.getEntityImporter(format.get(), is, clazz, null) : null;
      } catch (Exception e) {
        logger.error("error", e);
        return null;
      }
    }
docs: 构建实体导入者
  
  @param upload
  @param clazz