导出多级表头表格到Excel

方法一：用NPOI定义多级表头导出：

引用头：

using NPOI.DDF;
using NPOI.OpenXmlFormats.Wordprocessing;
using NPOI.HSSF.UserModel;
using NPOI.SS.UserModel;
using NPOI.SS.Util;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Web;
using System.Web.UI.WebControls;

定义方法：

public bool OutPutIMOrEXRSTExcel(DataTable dt)
        {
            bool Result = false;
            //在内存中生成一个Excel文件：
            HSSFWorkbook book = new HSSFWorkbook();
            ISheet sheet = book.CreateSheet("进出口退补税款统计表");

            sheet.DefaultRowHeight = 20 * 10;

            IRow row;
            ICell cell;
            int rowIndex = 0;
            int StartColIndex = 0;
            int colIndex = StartColIndex;

            //创建表头样式
            ICellStyle style = book.CreateCellStyle();
            style.Alignment = HorizontalAlignment.Center;
            style.WrapText = true;
            IFont font = book.CreateFont();
            font.FontHeightInPoints = 16;
            font.Boldweight = (short)NPOI.SS.UserModel.FontBoldWeight.Bold;
            font.FontName = "简体中文";
            style.SetFont(font);//HEAD 样式


            #region 定义表头
            //合并单元格
            int InOrEx = sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex + 2, colIndex, colIndex));//进出口标志
            var cellRangeAddress1 = sheet.GetMergedRegion(InOrEx);
            for (int i = cellRangeAddress1.FirstRow; i <= cellRangeAddress1.LastRow; i++)
            {
                row = sheet.CreateRow(rowIndex);
                //row.GetCell(0).CellStyle = style;

                cell = row.CreateCell(colIndex);
            }
            row = sheet.GetRow(rowIndex);
            cell = row.GetCell(colIndex);
            cell.SetCellValue("进出口标志");

            colIndex++;
            sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex, colIndex, colIndex + 2));
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("纠错项数");

            colIndex = colIndex + 3;
            sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex, colIndex, colIndex + 9));
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("退补税额");

            rowIndex++;

            colIndex = StartColIndex + 1;
            int involSup = sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex + 1, colIndex, colIndex));//涉及补税
            var cellRangeAddress4 = sheet.GetMergedRegion(involSup);
            for (int j = cellRangeAddress4.FirstRow; j <= cellRangeAddress4.LastRow; j++)
            {
                row = sheet.CreateRow(rowIndex);
                //row.GetCell(0).CellStyle = style;

                cell = row.CreateCell(colIndex);
            }
            row = sheet.GetRow(rowIndex);
            cell = row.GetCell(colIndex);
            cell.SetCellValue("涉及补税");

            colIndex++;
            int involRef = sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex + 1, colIndex, colIndex));//涉及退税
            var cellRangeAddress5 = sheet.GetMergedRegion(involRef);
            for (int j = cellRangeAddress5.FirstRow; j <= cellRangeAddress5.LastRow; j++)
            {
                cell = row.CreateCell(colIndex);
            }
            row = sheet.GetRow(rowIndex);
            cell = row.GetCell(colIndex);
            cell.SetCellValue("涉及退税");

            colIndex++;
            int NoRefSup = sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex + 1, colIndex, colIndex));//无退补税
            var cellRangeAddress6 = sheet.GetMergedRegion(NoRefSup);
            for (int j = cellRangeAddress6.FirstRow; j <= cellRangeAddress6.LastRow; j++)
            {
                cell = row.CreateCell(colIndex);
            }
            row = sheet.GetRow(rowIndex);
            cell = row.GetCell(colIndex);
            cell.SetCellValue("无退补税");


            colIndex++;
            sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex, colIndex, colIndex + 4));
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("补税");

            colIndex = colIndex + 5;
            sheet.AddMergedRegion(new CellRangeAddress(rowIndex, rowIndex, colIndex, colIndex + 4));
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("退税");

            //补税
            rowIndex++;
            row = sheet.CreateRow(rowIndex);
            //row.GetCell(0).CellStyle = style;

            colIndex = StartColIndex + 4;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("关税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("增值税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("消费税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("反倾销税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("协定关税");

            //退税
            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("关税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("增值税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("消费税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("反倾销税");

            colIndex++;
            cell = row.CreateCell(colIndex);
            cell.SetCellValue("协定关税");
            colIndex++;

            #endregion

            #region 定义表体并赋值
            rowIndex++;
            foreach (DataRow dr in dt.Rows)
            {
                colIndex = StartColIndex;
                row = sheet.CreateRow(rowIndex);
                foreach (DataColumn dc in dt.Columns)
                {
                    cell = row.CreateCell(colIndex);
                    cell.SetCellValue(dr[colIndex].ToString());

                    colIndex++;
                }
                rowIndex++;
            }
            #endregion

            //Excel 输出
            string fileName = @"ExitClassifiedCorrectionReport.xls";
            try
            {
                HttpResponse rs = System.Web.HttpContext.Current.Response;
                rs.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
                rs.AppendHeader("Content-Disposition", "attachment;filename=" + fileName);
                rs.ContentType = "application/ms-excel";
                using (MemoryStream ms = new MemoryStream())
                {
                    book.Write(ms);
                    rs.BinaryWrite(ms.ToArray());
                    ms.Flush();
                }
            }
            catch (Exception ex)
            {
                LogHelper.Write(ex);
            }
            return Result;
        }

方法二：直接调用html代码导出table（适用于数据量较少的table）：

JS代码：

//导出table到Excel
function OutPutTab() {
        var html = document.getElementById("myTable").outerHTML;
        var shtml = htmlEncode(html);

        $("input[name='hHtml']").val(shtml);
        //表单提交
        document.getElementById("OutPutTab").submit();
}
//html代码编码（否则报字符错误）
function htmlEncode(value) {
    return $('<div/>').text(value).html();
}

后台导出代码：

 /// <summary>
        /// 下载统计表数据
        /// </summary>
        /// <param name="form"></param>
        /// <returns></returns>
        [HttpPost]
        public FileResult ExportExcel(FormCollection form)
        {
            //第一种:使用FileContentResult
            string content = Request.Form["hHtml"];
            string strHtml = form["hHtml"];
            strHtml = HttpUtility.HtmlDecode(strHtml);//Html解码
            byte[] fileContents = Encoding.UTF8.GetBytes(strHtml);
            string filename = DateTime.Now.ToString("yyyyMMddHHmmss");
            return File(fileContents, "application/ms-excel", "进出口退补税额统计表" + filename + ".xls");

            //第二种:使用FileStreamResult
            var fileStream = new MemoryStream(fileContents);
            return File(fileStream, "application/ms-excel", "fileStream.xls");

            //第三种:使用FilePathResult
            //服务器上首先必须要有这个Excel文件,然会通过Server.MapPath获取路径返回.
            var fileName = Server.MapPath("~/uploads/选题信息导入模板.xls");
            return File(fileName, "application/ms-excel", "fileName.xls");

        }

遇到的问题及解决方案：

1、中文字符变成乱码：

导出的Excel中文字符变成乱码，网上查询到可能是编码格式的问题，通过查看网页源码发现是“UTF-8”的格式。所以我一直认为解码的默认格式就是“UTF-8”，

所以在转成byte[] 流时就一直用的默认的编码方式byte[] fileContents = Encoding.Default.GetBytes(strHtml);

转码成GB2312的byte[]方式：byte[] buffer= Encoding.GetEncoding("GB2312").GetBytes(strHtml); 

或者转成字符串：string str=Encoding.GetEncoding("GB2312").GetString(buffer);

2、IE8下文件名丢失。后缀名丢失。

ie不支持中文文件名输出。将文件名变成英文就可以了。