安装NOPI包

 //导入数据 
  
 public static DataTable Import(string filePath,string sheetName = "")         {             var excelType = Path.GetExtension(filePath).ToLower();             DataTable dt;             using (var stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))             {                 dt = ImportExcel(stream, excelType, sheetName);             }             return dt;       
        } 
private static DataTable ImportExcel(Stream stream, string type, string sheetName)
        {
  DataTable dt = new DataTable();
 IWorkbook workbook ;
 try
 {
 if (type != ".xls")
 {
    workbook = new XSSFWorkbook(stream);
 }
 else
 {
 workbook = new HSSFWorkbook(stream);
 }
 ISheet sheet = null;
 //获取工作表 默认取第一张
 if (string.IsNullOrWhiteSpace(sheetName))
 sheet = workbook.GetSheetAt(0);
 else
 sheet = workbook.GetSheet(sheetName);
 if (sheet == null)
  return null;
 IEnumerator rows = sheet.GetRowEnumerator();
  #region 获取表头
  IRow headerRow = sheet.GetRow(0);
 int cellCount = headerRow.LastCellNum;
  for (int j = 0; j < cellCount; j++)
  {
 ICell cell = headerRow.GetCell(j);
 if (cell != null)
  {
 dt.Columns.Add(cell.ToString());
    }
  else
  {
  dt.Columns.Add("");
   }
 }
 endregion
 #region 获取内容
  for (int i = (sheet.FirstRowNum + 1); i <= sheet.LastRowNum; i++)    {  IRow row = sheet.GetRow(i);  DataRow dataRow = dt.NewRow();  for (int j = row.FirstCellNum; j < cellCount; j++) { if (row.GetCell(j) != null) { //判断单元格是否为日期格式 if (row.GetCell(j).CellType == NPOI.SS.UserModel.CellType.Numeric && HSSFDateUtil.IsCellDateFormatted(row.GetCell(j))) { if (row.GetCell(j).DateCellValue.Year >= 1970)
 {
 dataRow[j] = row.GetCell(j).DateCellValue.ToString();
  }
 else
 {
 dataRow[j] = row.GetCell(j).ToString();
 }
  }
  else
   {
  dataRow[j] = row.GetCell(j).ToString();
   }
 }
  }
 dt.Rows.Add(dataRow);
 }
  #endregion
    }
 catch (Exception ex)
 {
  dt = null;
 }
 finally
 {
 if (stream != null)
 {
                     stream.Close();
                     stream.Dispose();
                 }
             }
             return dt;
         }

//导出数据
protected void ExportExcel(DataTable dt)
        {
            HttpContext curContext = System.Web.HttpContext.Current;
            //设置编码及附件格式 
            curContext.Response.ContentType = "application/vnd.ms-excel";
            curContext.Response.ContentEncoding = Encoding.UTF8;
            curContext.Response.Charset = "";
            string fullName = HttpUtility.UrlEncode("FileName.xlsx", Encoding.UTF8);
            curContext.Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(fullName, Encoding.UTF8));
            //attachment后面是分号
            byte[] data = TableToExcel(dt, fullName).GetBuffer();
            curContext.Response.BinaryWrite(TableToExcel(dt, fullName).GetBuffer());
            curContext.Response.End();
        }
        public MemoryStream TableToExcel(DataTable dt, string file)
        {
            //创建workbook 
            IWorkbook workbook;
            string fileExt = Path.GetExtension(file).ToLower();
            if (fileExt == ".xlsx")
                workbook = new XSSFWorkbook();
            else if (fileExt == ".xls")
                workbook = new HSSFWorkbook();
            else workbook = null;
            //创建sheet 
            ISheet sheet = workbook.CreateSheet("Sheet1");
            //表头 
            IRow headrow = sheet.CreateRow(0);
            for (int i = 0; i < dt.Columns.Count; i++)
            {
                ICell headcell = headrow.CreateCell(i);
                headcell.SetCellValue(dt.Columns[i].ColumnName);
            }
            //表内数据 
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                IRow row = sheet.CreateRow(i + 1);
                for (int j = 0; j < dt.Columns.Count; j++)
                {
                    ICell cell = row.CreateCell(j);
                    cell.SetCellValue(dt.Rows[i][j].ToString());
                }
            }
            //转化为字节数组 
            MemoryStream ms = new MemoryStream();
            workbook.Write(ms);
            ms.Flush();
            //ms.Position = 0;
            return ms;
        }