public class NpoiMemoryStream : MemoryStream

    {

        public NpoiMemoryStream()

        {

            AllowClose = true;

        }

        public bool AllowClose { get; set; }

        public override void Close()

        {

            if (AllowClose)

                base.Close();

        }

    }

  public ActionResult Export()

        {

            int orderId = base.Id;

            Orders order = OrdersModel.GetInstance.GetById(orderId);

            var workbook = new XSSFWorkbook(Server.MapPath("~/Template/order.xlsx"));

            var sheet = workbook.GetSheetAt();

            IRow row = sheet.CreateRow();

            row.CreateCell().SetCellValue("货号");

            row.CreateCell().SetCellValue("品名");

            row.CreateCell().SetCellValue("颜色");

            string fname = string.Format("{0}.xlsx", order.OrderNo);

            //导出Excel文件的方法

            var ms = new NpoiMemoryStream();

            ms.AllowClose = false;

            workbook.Write(ms);

            ms.Flush();

            ms.Seek(, SeekOrigin.Begin);

            ms.AllowClose = true;

            return File(ms, "application/vnd.ms-excel", fname);

        }