NPOI读取Excel文件

string strExtName = Path.GetExtension(strFilePath);

                if (strExtName.Equals(".xls") || strExtName.Equals(".xlsx"))
                {
                    using (FileStream file = new FileStream(strFilePath, FileMode.Open, FileAccess.Read))
                    {
                        ISheet sheet = null;
                        if (strExtName.Equals(".xls"))
                        {
                            HSSFWorkbook workbook = new HSSFWorkbook(file);
                            sheet = workbook.GetSheetAt(iSheetIndex);
                        }
                        if (strExtName.Equals(".xlsx"))
                        {
                            XSSFWorkbook workbook = new XSSFWorkbook(file);
                            sheet = workbook.GetSheetAt(iSheetIndex);
                        }
            }
                }