NPOI读取Excel文件

public class ExcelOperator
    {
        public static List<DataTable> Read(string fileName)
        {
            List<DataTable> tables = new List<DataTable>();
            if (!File.Exists(fileName))
                return tables;
            var fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
            IWorkbook workbook = null;
            if (fileName.IndexOf(".xlsx") > 0)
            {
                // 2007版本
                workbook = new XSSFWorkbook(fs);
            }
            else if (fileName.IndexOf(".xls") > 0)
            {
                // 2003版本
                workbook = new HSSFWorkbook(fs);
            }

            var workbooks = workbook.GetEnumerator();
            while (workbooks.MoveNext())
            {
                ISheet sheet = workbooks.Current as ISheet;
                DataTable dt = new DataTable(sheet.SheetName);
                var rows = sheet.GetRowEnumerator();
                while (rows.MoveNext())
                {
                    IRow row = rows.Current as IRow;
                    if (row.RowNum == 0)
                    {
                        row.Cells.ForEach(cell =>
                        {
                            dt.Columns.Add(cell.StringCellValue);
                        });
                    }
                    else
                    {
                        var dr = dt.NewRow();
                        for (int i = 0; i < row.Cells.Count; i++)
                        {
                            dr[i] = row.Cells[i].ToString();
                        }
                        dt.Rows.Add(dr);
                    }
                }

                tables.Add(dt);
            }
            return tables;
        }
    }

public static DataTable ReadExcel(string fileName, string sheetname)
        {
            if (!File.Exists(fileName))
                return null;
            var fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
            IWorkbook workbook = null;
            if (fileName.IndexOf(".xlsx") > 0)
            {
                // 2007版本
                workbook = new XSSFWorkbook(fs);
            }
            else if (fileName.IndexOf(".xls") > 0)
            {
                // 2003版本
                workbook = new HSSFWorkbook(fs);
            }
            ISheet sheet = workbook.GetSheet(sheetname);
            DataTable dt = new DataTable();
            var rows = sheet.GetRowEnumerator();
            while (rows.MoveNext())
            {
                IRow row = rows.Current as IRow;
                if (row.RowNum == 0)
                {
                    row.Cells.ForEach(cell =>
                    {
                        dt.Columns.Add(cell.StringCellValue);
                    });
                }
                else
                {
                    var dr = dt.NewRow();
                    for (int i = 0; i < row.Cells.Count; i++)
                    {
                        dr[i] = row.Cells[i].ToString();
                    }
                    dt.Rows.Add(dr);
                }
            }
            return dt;
        }