/// <summary>
  /// 根據(jù)Excel格式讀取Excel
  /// </summary>
  /// <param name="stream">文件流</param>
  /// <param name="type">Excel格式枚舉類型，xls/xlsx</param>
  /// <param name="sheetName">表名，默認取第一張</param>
  /// <returns>DataTable</returns>
  private static DataTable ImportExcel(Stream stream, ExcelExtType type, string sheetName)
  {
    DataTable dt = new DataTable();
    IWorkbook workbook;
    try
    {
      //xls使用HSSFWorkbook類實現(xiàn)，xlsx使用XSSFWorkbook類實現(xiàn)
      switch (type)
      {
        case ExcelExtType.xlsx:
          workbook = new XSSFWorkbook(stream);
          break;
        default:
          workbook = new HSSFWorkbook(stream);
          break;
      }
      ISheet sheet = null;
      //獲取工作表 默認取第一張
      if (string.IsNullOrWhiteSpace(sheetName))
        sheet = workbook.GetSheetAt(0);
      else
        sheet = workbook.GetSheet(sheetName);

      if (sheet == null)
        return null;
      IEnumerator rows = sheet.GetRowEnumerator();
      #region 獲取表頭
      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 獲取內(nèi)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)
          {
            //判斷單元格是否為日期格式
            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;
  }

  /// <summary>
  /// 上傳Excel導入
  /// </summary>
  /// <param name="file">上載文件對象</param>
  /// <param name="errorMsg">錯誤信息</param>
  /// <param name="sheetName">表名，默認取第一張</param>
  /// <returns></returns>
  public static DataTable Import(System.Web.HttpPostedFileBase file, ref string errorMsg, string sheetName = "")
  {
    if (file == null || file.InputStream == null || file.InputStream.Length == 0)
    {
      errorMsg = "請選擇要導入的Excel文件";
      return null;
    }
    var excelType = GetExcelFileType(file.FileName);
    if (excelType == null)
    {
      errorMsg = "請選擇正確的Excel文件";
      return null;
    }
    using (var stream = new MemoryStream())
    {
      file.InputStream.Position = 0;
      file.InputStream.CopyTo(stream);
      var dt = ImportExcel(stream, excelType.Value, sheetName);
      if (dt == null)
        errorMsg = "導入失敗,請選擇正確的Excel文件";
      return dt;
    }
  }

  /// <summary>
  /// 根據(jù)文件路徑導入Excel
  /// </summary>
  /// <param name="filePath"></param>
  /// <param name="errorMsg">錯誤信息</param>
  /// <param name="sheetName">表名，默認取第一張</param>
  /// <returns>可能為null的DataTable</returns>
  public static DataTable Import(string filePath, ref string errorMsg, string sheetName = "")
  {
    var excelType = GetExcelFileType(filePath);
    if (GetExcelFileType(filePath) == null)
    {
      errorMsg = "請選擇正確的Excel文件";
      return null;
    }
    if (!File.Exists(filePath))
    {
      errorMsg = "沒有找到要導入的Excel文件";
      return null;
    }
    DataTable dt;
    using (var stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    {
      dt = ImportExcel(stream, excelType.Value, sheetName);
    }
    if (dt == null)
      errorMsg = "導入失敗,請選擇正確的Excel文件";
    return dt;
  }