c# 后台 导出EXCEL方法

------先上代码------

/// <summary>
        /// 生成excel文件流
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="filePath"></param>
        /// <param name="styleType">样式格式</param>
        /// <param name="sheetIndex"></param>
        public static void DataTableToExcel(DataTable dt, string filePath, HorizontalAlignment styleType, int sheetIndex = 0)
        {
            IWorkbook workbook = null;
            try
            {
                using (FileStream file = new FileStream(filePath, FileMode.Open, FileAccess.Read))
                {
                    workbook = new XSSFWorkbook(file);
                    ISheet sheet = workbook.GetSheetAt(sheetIndex);
                    ICellStyle headerCellStyle = workbook.CreateCellStyle();
                    headerCellStyle.BorderBottom = BorderStyle.Thin;
                    headerCellStyle.BorderLeft = BorderStyle.Thin;
                    headerCellStyle.BorderRight = BorderStyle.Thin;
                    headerCellStyle.BorderTop = BorderStyle.Thin;

                    headerCellStyle.Alignment = styleType;//设置title样式(居中,靠右)
                    IFont headerFont = workbook.CreateFont();
                    headerFont.FontHeightInPoints = 11;
                    headerFont.Boldweight = (short)FontBoldWeight.Bold;
                    headerCellStyle.SetFont(headerFont);

                    int colIndex = 0;
                    IRow headerRow = sheet.CreateRow(0);
                    foreach (DataColumn dc in dt.Columns)
                    {
                        ICell cell = headerRow.CreateCell(colIndex);
                        cell.SetCellValue(dc.ColumnName);
                        cell.CellStyle = headerCellStyle;
                        colIndex++;
                    }
                    IFont cellFont = workbook.CreateFont();
                    cellFont.FontHeightInPoints = 11;
                    cellFont.Boldweight = (short)FontBoldWeight.Normal;

                    ICellStyle cellStyleNumber = workbook.CreateCellStyle();
                    cellStyleNumber.BorderBottom = BorderStyle.Thin;
                    cellStyleNumber.BorderLeft = BorderStyle.Thin;
                    cellStyleNumber.BorderRight = BorderStyle.Thin;
                    cellStyleNumber.BorderTop = BorderStyle.Thin;
                    cellStyleNumber.SetFont(cellFont);
                    IDataFormat dataFormatNumber = workbook.CreateDataFormat();
                    cellStyleNumber.DataFormat = dataFormatNumber.GetFormat("0");

                    ICellStyle cellStyleNumberic = workbook.CreateCellStyle();
                    cellStyleNumberic.BorderBottom = BorderStyle.Thin;
                    cellStyleNumberic.BorderLeft = BorderStyle.Thin;
                    cellStyleNumberic.BorderRight = BorderStyle.Thin;
                    cellStyleNumberic.BorderTop = BorderStyle.Thin;
                    cellStyleNumberic.SetFont(cellFont);
                    IDataFormat dataFormatNumberic = workbook.CreateDataFormat();
                    cellStyleNumberic.DataFormat = dataFormatNumberic.GetFormat("0.00");

                    ICellStyle cellStyleDateTime = workbook.CreateCellStyle();
                    cellStyleDateTime.BorderBottom = BorderStyle.Thin;
                    cellStyleDateTime.BorderLeft = BorderStyle.Thin;
                    cellStyleDateTime.BorderRight = BorderStyle.Thin;
                    cellStyleDateTime.BorderTop = BorderStyle.Thin;
                    cellStyleDateTime.SetFont(cellFont);
                    IDataFormat dataFormatDateTime = workbook.CreateDataFormat();
                    cellStyleDateTime.DataFormat = dataFormatDateTime.GetFormat("MM/dd/yyyy");

                    ICellStyle cellStyleText = workbook.CreateCellStyle();
                    cellStyleText.BorderBottom = BorderStyle.Thin;
                    cellStyleText.BorderLeft = BorderStyle.Thin;
                    cellStyleText.BorderRight = BorderStyle.Thin;
                    cellStyleText.BorderTop = BorderStyle.Thin;
                    cellStyleText.SetFont(cellFont);
                    IDataFormat dataFormatText = workbook.CreateDataFormat();
                    //cellStyleText.DataFormat = dataFormatText.GetFormat("@");

                    int rowIndex = 1;
                    int cellIndex = 0;
                    foreach (DataRow dr in dt.Rows)
                    {
                        IRow dataRow = sheet.CreateRow(rowIndex);
                        foreach (DataColumn dc in dt.Columns)
                        {
                            ICell cell = dataRow.CreateCell(cellIndex);
                            Int64 number = 0;
                            double numberic = 0;
                            DateTime dateTime = new DateTime();

                            string columnValue = dr[dc].ToString();
                            if (Int64.TryParse(columnValue, out number))
                            {
                                cell.SetCellValue(number);
                                cellStyleNumber.Alignment = styleType;
                                cell.CellStyle = cellStyleNumber;
                            }
                            else if (double.TryParse(columnValue, out numberic) && columnValue.Contains('.'))
                            {
                                cell.SetCellValue(numberic);
                                cellStyleNumber.Alignment = styleType;
                                cell.CellStyle = cellStyleNumberic;
                            }
                            else if (DateTime.TryParse(columnValue, out dateTime))
                            {
                                if (dc.ToString().Trim().ToLower()== "createtime")
                                {
                                    if (dateTime.ToString("yyyy-MM-dd") == "0001-01-01")
                                    {
                                        cell.SetCellValue("");
                                    }
                                    else
                                    {
                                        cell.SetCellValue(dateTime.ToString("MM/dd/yyyy HH:mm:ss"));
                                    }
                                }
                                else
                                {
                                    if (dateTime.ToString("yyyy-MM-dd") == "0001-01-01")
                                    {
                                        cell.SetCellValue("");
                                    }
                                    else
                                    {
                                        cell.SetCellValue(dateTime.ToString("MM/dd/yyyy"));
                                    }
                                }
                                cellStyleDateTime.Alignment = styleType;
                                cell.CellStyle = cellStyleDateTime;
                            }
                            else
                            {
                                cell.SetCellValue(columnValue);
                                cellStyleText.Alignment = styleType;
                                cell.CellStyle = cellStyleText;
                            }
                            cellIndex++;
                        }
                        cellIndex = 0;
                        rowIndex++;
                    }
                    //for (int i = 0; i < colIndex; i++)
                    //{
                    //    sheet.AutoSizeColumn(i);
                    //}
                    MemoryStream ms = new MemoryStream();
                    workbook.Write(ms);
                    ms.Flush();
                    using (FileStream saveFile = new FileStream(filePath, FileMode.Create, FileAccess.Write))
                    {
                        byte[] data = ms.ToArray();
                        saveFile.Write(data, 0, data.Length);
                        saveFile.Flush();
                        data = null;
                    }
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                workbook = null;
            }
        }

------------对上面方法调用---------------
/// <summary>
        /// 下载文件
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="fileName"></param>
        /// <param name="sheetName"></param>
        public static string DownLoadExcel(DataTable dt, string fileName, string styleType = "")
        {
            //当前日文件夹
            string dateString = System.DateTime.Now.ToString("yyyyMMdd");
            //删除其他日期文件夹
            DirectoryInfo dir = new DirectoryInfo(HostingEnvironment.MapPath("~/TemparyFile"));
            FileSystemInfo[] fileinfo = dir.GetFileSystemInfos();  //返回目录中所有文件和子目录
            foreach (FileSystemInfo i in fileinfo)
            {
                if (i is DirectoryInfo && !i.Name.Equals(dateString) && !i.Name.ToLower().Equals("userfile")) //判断是否文件夹
                {
                    DirectoryInfo subdir = new DirectoryInfo(i.FullName);
                    subdir.Delete(true);          //删除子目录和文件
                }
            }

            //无当天文件夹时创建文件夹
            if (!Directory.Exists(HostingEnvironment.MapPath("~/TemparyFile/" + dateString)))
            {
                Directory.CreateDirectory(HostingEnvironment.MapPath("~/TemparyFile/" + dateString));
            }


            string sourceFile = HostingEnvironment.MapPath("~/TemparyFile/ExcelTemplate.xlsx");
            var date = DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + DateTime.Now.Day.ToString() + DateTime.Now.Hour.ToString() + DateTime.Now.Minute.ToString() + DateTime.Now.Second.ToString();
            //string destFileName = fileName+"-" + Guid.NewGuid() + ".xlsx";
            string destFileName = fileName + "_" + date + ".xlsx";
            string destFilePath = HostingEnvironment.MapPath("~/TemparyFile/" + dateString) + "/" + destFileName;
            File.Copy(sourceFile, destFilePath);


            switch (styleType.ToLower())
            {
                case "center":
                    ExcelHandle.DataTableToExcel(dt, destFilePath, NPOI.SS.UserModel.HorizontalAlignment.Center);
                    break;
                case "right":
                    ExcelHandle.DataTableToExcel(dt, destFilePath, NPOI.SS.UserModel.HorizontalAlignment.Right);
                    break;
                default:
                    ExcelHandle.DataTableToExcel(dt, destFilePath);
                    break;
            }

            return "/TemparyFile/" + dateString + "/" + destFileName;
        }