Excel導入Npoi支持xls/xlsx

public static DataSet Import(string strFileName)
        {
            try
            {
                DataSet ds = new DataSet();
                NPOI.HSSF.UserModel.HSSFWorkbook hssfworkbook = null;
                NPOI.XSSF.UserModel.XSSFWorkbook xssfworkbook = null;
                NPOI.SS.UserModel.ISheet sheet = null;
                bool bo = true;
                using (FileStream file = new FileStream(strFileName, FileMode.Open, FileAccess.Read))
                {
                    if (strFileName.Last() == 's')
                        hssfworkbook = new NPOI.HSSF.UserModel.HSSFWorkbook(file);
                    else
                    {
                        bo = false;
                        xssfworkbook = new NPOI.XSSF.UserModel.XSSFWorkbook(file);
                    }
                }
                for (int sh = 0; sh < (bo ? hssfworkbook.Count : xssfworkbook.Count); sh++)
                {
                    sheet = bo ? hssfworkbook.GetSheetAt(sh) : xssfworkbook.GetSheetAt(sh); ;
                    DataTable dt = new DataTable();
                    dt.TableName = sheet.SheetName;
                    System.Collections.IEnumerator rows = sheet.GetRowEnumerator();
                    NPOI.SS.UserModel.IRow headerRow = sheet.GetRow(0);
                    int cellCount = headerRow.LastCellNum;
                    for (int j = 0; j < cellCount; j++)
                    {
                        NPOI.SS.UserModel.ICell cell = headerRow.GetCell(j);
                        dt.Columns.Add(cell.ToString());
                    }
                    for (int i = (sheet.FirstRowNum + 1); i <= sheet.LastRowNum; i++)
                    {
                        NPOI.SS.UserModel.IRow row = sheet.GetRow(i);
                        DataRow dataRow = dt.NewRow();

                        for (int j = row.FirstCellNum; j < cellCount; j++)
                        {
                            if (row.GetCell(j) != null)
                                dataRow[j] = row.GetCell(j).ToString();
                        }
                        dt.Rows.Add(dataRow);
                    }
                    ds.Tables.Add(dt);//添加所有工作簿內容
                }
                return ds;
            }
            catch (Exception ex)
            {
                throw new Exception("讀取Excel異常" + ex);
            }
        }