NPOI 2.1.3.1版本读取excel 2003 2007版本文件

  var ext = Path.GetExtension(filename).ToLower();
        using (FileStream fs = File.OpenRead(filename))
                {
                    IWorkbook wk;
                    if (ext.Contains("xlsx"))
                        wk = new XSSFWorkbook(fs);
                    else
                        wk = new HSSFWorkbook(fs);
                    ISheet sheet = wk.GetSheetAt(0);
 
                    for (int j = 0; j <= sheet.LastRowNum; j++)  //LastRowNum 是当前表的总行数
                    {
                        IRow row = sheet.GetRow(j);  //读取当前行数据
                        if (row == null)
                            return;
                        ICell cell = row.GetCell(0);  //当前表格
                        if (cell == null)
                            return;                                                 
                    }
                }