Java导出Excel，提示格式与文件扩展名不一致

后台代码，这是基础方法，还要根据使用调用

   public static void exportExcel(HttpServletResponse response, String sheetName, String fileName, String[] header, List content)
           throws IOException {

      // 清空response
      response.reset();
      // 设置response的Header
      response.setHeader("Content-disposition",
              "attachment;filename=" + new String(fileName.getBytes("gbk"), "iso8859-1") + ".xlsx");
      response.setContentType("application/vnd.ms-excel;charset=gb2312");
      Sheet sheet = new Sheet(1, 0);
      sheet.setSheetName(sheetName);
      // 设置自适应宽度
      sheet.setAutoWidth(Boolean.TRUE);
      // 设置表头
      List> list = new ArrayList<>();
      for (int i = 0; i < header.length; i++) {
         list.add(Collections.singletonList(header[i]));
      }
      sheet.setHead(list);
      OutputStream outputStream = null;
      ExcelWriter writer = null;
      try {
         outputStream = new BufferedOutputStream(response.getOutputStream());
         writer = EasyExcelFactory.getWriter(outputStream);
         List> data = new ArrayList>();
         for (int i = 0; i < content.size(); i++) {
            List