參考地址:https://www.cnblogs.com/shiliang199508/p/7365312.html

/// <summary>
        /// create 2016-11-30 by sly 
        /// 將DataTable資料匯入到excel中   此方法直接返回檔案給瀏覽器下載
        /// </summary>
        /// <param name="data">要匯入的資料</param>
        /// <param name="isColumnWritten">DataTable的列名是否要匯入</param>
 

        /// <param name="sheetName">要匯入的excel的sheet的名稱</param>
        /// <param name="widthDic">要設定的寬度(key 列下標,val 寬度大小)</param>
        /// <returns></returns>
        public int DataTableToExcel(DataTable data, string sheetName, bool isColumnWritten, Dictionary<int, int
 
> widthDic = null)
        {
            int i = 0;
            int j = 0;
            int count = 0;
            ISheet sheet = null;

            MemoryStream file = new MemoryStream();

            if (fileName.IndexOf(".xlsx") > 0) //2007版本
                workbook = new XSSFWorkbook();
            
 
else
                if (fileName.IndexOf(".xls") > 0) // 2003版本
                workbook = new HSSFWorkbook();

            try
            {
                if (workbook != null)
                {
                    sheet = workbook.CreateSheet(sheetName);

                    //設定所有列寬
                    for (int l = 0; l <= data.Rows.Count; l++)
                    {
                        sheet.DefaultColumnWidth = 12;
                    }

                    if (widthDic != null)
                    {
                        //設定自定義寬度
                        foreach (var item in widthDic)
                        {
                            sheet.SetColumnWidth(item.Key, item.Value);
                        }
                    }
                }
                else
                {
                    return -1;
                }

                if (isColumnWritten == true) //寫入DataTable的列名
                {
                    IRow row = sheet.CreateRow(0);
                    for (j = 0; j < data.Columns.Count; ++j)
                    {
                        row.CreateCell(j).SetCellValue(data.Columns[j].ColumnName);
                    }
                    count = 1;
                }
                else
                {
                    count = 0;
                }
                int outRes = -1;

                for (i = 0; i < data.Rows.Count; ++i)
                {
                    IRow row = sheet.CreateRow(count);
                    for (j = 0; j < data.Columns.Count; ++j)
                    {
                        if (int.TryParse(data.Rows[i][j].ToString(), out outRes))
                        {
                            row.CreateCell(j).SetCellValue(Convert.ToInt32(data.Rows[i][j].ToString()));
                        }
                        else
                        {
                            if (!string.IsNullOrEmpty(data.Rows[i][j].ToString()) && data.Rows[i][j].ToString().Length > 10)
                            {
                                if ((data.Rows[i][j].ToString().Substring(0, 7) == "http://" || data.Rows[i][j].ToString().Substring(0, 8) == "https://"))
                                {
                                    var TCell = row.CreateCell(j);
                                    HSSFHyperlink link = new HSSFHyperlink(HyperlinkType.Url);//建一個HSSFHyperlink實體，指明連結型別為URL  
                                    TCell.SetCellValue(data.Rows[i][j].ToString());
                                    link.Address = data.Rows[i][j].ToString();//給HSSFHyperlink的地址賦值                                                                      
                                    TCell.Hyperlink = link;
                                }
                                else
                                {
                                    row.CreateCell(j).SetCellValue(data.Rows[i][j].ToString());
                                }
                            }
                            else
                            {
                                row.CreateCell(j).SetCellValue(data.Rows[i][j].ToString());
                            }
                        }
                    }
                    ++count;
                }
                workbook.Write(file); //寫入到excel

                var context = System.Web.HttpContext.Current;
                context.Response.ContentType = "application/vnd.ms-excel";
                context.Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", fileName));
                context.Response.Clear();
                context.Response.BinaryWrite(file.GetBuffer());
                context.Response.End();


                return count;
            }
            catch (Exception ex)
            {
                return -2;
            }
        }

/// <summary>        
        /// 將excel中的資料匯入到DataTable中
        /// </summary>
        /// <param name="sheetName">excel工作薄sheet的名稱</param>
        /// <param name="isFirstRowColumn">第一行是否是DataTable的列名</param>
        /// <returns></returns>
        public DataTable ExcelToDataTable(string sheetName, bool isFirstRowColumn)
        {
            ISheet sheet = null;
            DataTable data = new DataTable();
            int startRow = 0;
            try
            {
                fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
                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);

                if (sheetName != null)
                {
                    sheet = workbook.GetSheet(sheetName);
                    if (sheet == null) //如果沒有找到指定的sheetName對應的sheet，則嘗試獲取第一個sheet
                    {
                        sheet = workbook.GetSheetAt(0);
                    }
                }
                else
                {
                    sheet = workbook.GetSheetAt(0);
                }
                if (sheet != null)
                {
                    IRow firstRow = sheet.GetRow(0);
                    int cellCount = firstRow.LastCellNum; //一行最後一個cell的編號 即總的列數

                    if (isFirstRowColumn)
                    {
                        for (int i = firstRow.FirstCellNum; i < cellCount; ++i)
                        {
                            ICell cell = firstRow.GetCell(i);
                            if (cell != null)
                            {
                                string cellValue = cell.StringCellValue;
                                if (cellValue != null)
                                {
                                    DataColumn column = new DataColumn(cellValue);
                                    data.Columns.Add(column);
                                }
                            }
                        }
                        startRow = sheet.FirstRowNum + 1;
                    }
                    else
                    {
                        startRow = sheet.FirstRowNum;
                    }

                    //最後一列的標號
                    int rowCount = sheet.LastRowNum;
                    for (int i = startRow; i <= rowCount; ++i)
                    {
                        IRow row = sheet.GetRow(i);
                        if (row == null) continue; //沒有資料的行預設是null　　　　　　　

                        DataRow dataRow = data.NewRow();
                        for (int j = row.FirstCellNum; j < cellCount; ++j)
                        {
                            if (row.GetCell(j) != null) //同理，沒有資料的單元格都預設是null
                                dataRow[j] = row.GetCell(j).ToString();
                        }
                        data.Rows.Add(dataRow);
                    }
                }

                return data;
            }
            catch (Exception ex)
            {                
                return null;
            }
        }