code: public Attachment attachFile(long sheetId, long rowId, InputStream inputStream, String contentType, long contentLength, String attachmentName)
              throws SmartsheetException {
          Util.throwIfNull(inputStream, contentType);
          return super.attachFile("sheets/" + sheetId + "/rows/" + rowId + "/attachments", inputStream, contentType, contentLength, attachmentName);
      }
docs: Attach file for simple upload.
  
  @param sheetId the sheet id
  @param rowId the row id
  @param contentType the content type
  @param contentLength the content length
  @param attachmentName the name of the attachment
  @return the attachment
  @throws FileNotFoundException the file not found exception
  @throws SmartsheetException the smartsheet exception
  @throws UnsupportedEncodingException the unsupported encoding exception