使用NPOI导入Excel注意日期格式和数字格式

//使用NPOI导入Excel
    public static DataTable importExcelToDataSetUsingNPOI(string FilePath, string fileName)
    {
        DataSet myDs = new DataSet();
        DataTable dt = new DataTable("mytable");

        myDs.Tables.Add(dt);
        DataRow myRow;
        myDs.Clear();

        try
        {
            using (Stream stream = new FileStream(FilePath, FileMode.Open, FileAccess.Read))
            {
                HSSFWorkbook wk = new HSSFWorkbook(stream);

                ISheet sheet = wk.GetSheetAt();   //读取当前表数据 只读取第一个sheet

                int rowsint = sheet.LastRowNum;
                for (int y = ; y <= rowsint; y++)
                {
                    //Execel第一行是标题，不是要导入数据库的数据
                    IRow row = sheet.GetRow(y);  //读取当前行数据
                    if (row != null)
                    {
                        int columnsint = row.LastCellNum;
                        if (y == )//第一行，标题
                        {
                            for (int m = ; m < columnsint; m++)
                            {
                                dt.Columns.Add("F" + m.ToString(), System.Type.GetType("System.String"));
                            }
                        }
                        else
                        {
                            myRow = myDs.Tables["mytable"].NewRow();
                            for (int j = ; j < columnsint; j++)
                            {
                                if (j == )
                                {

                                }
                                if (row.GetCell(j).CellType == CellType.NUMERIC)//数字类型
                                {
                                    string columnname = "F" + j.ToString();
                                    if (DateUtil.IsValidExcelDate(row.GetCell(j).NumericCellValue) && DateUtil.IsCellDateFormatted(row.GetCell(j)))
                                    {
                                        DateTime D = row.GetCell(j).DateCellValue;
                                        myRow[columnname] = (D.ToString().Length ==  || D.ToString().Contains("#")) ? " " : D.ToString();
                                    }
                                    else
                                    {
                                        double strValue = row.GetCell(j).NumericCellValue;
                                        myRow[columnname] = (strValue.ToString().Length ==  || strValue.ToString().Contains("#")) ? " " : strValue.ToString();
                                    }
                                }
                                else
                                {
                                    string strValue = row.GetCell(j).StringCellValue;
                                    string columnname = "F" + j.ToString();
                                    myRow[columnname] = (strValue.Length ==  || strValue.Contains("#")) ? " " : strValue;
                                }
                            }
                            try
                            {
                                myDs.Tables["mytable"].Rows.Add(myRow);
                            }
                            catch { }
                        }
                    }
                }
            }
        }
        catch (Exception ex)
        {
            Debug.WriteLine(ex.Message);
        }
        return myDs.Tables["mytable"];
    }