npoi生成excel流并在客户端下载（html+后台 ）

//前端页面
<body>
    <input type="button" value="导出Excel" class="button" id="btnjbntExport" runat="server" onclick="Exportjbnt()"/>
    <table class="table">
        <thead>
            <th colspan="3">基本农田保护区面积统计表(公顷)</th>
        </thead>
        <tbody>
            <tr>
                <td>基本农田占用总面积</td>
                <td id="JBNTZMJ">0.00</td>
            </tr> 

        </tbody>

    </table>
    <form id="jbntform" action="./GisUtility/GeometryHelper.ashx" method="post"> //用js操作文件流，所以用form的post方法是一个不错的选择
         <input type="hidden" id="jbntarea" name="jbntarea" />//传递参数到后台
         <input type="hidden" id="jbnttype" name="jbnttype" />
    </form>
</body>

//加载前端面前先加载包涵下面方法的js文件

function Exportjbnt() {
    var area = GetJbntValue();
    $("#jbnttype").val("exportjbnt");
    $("#jbntarea").val(area);
    $("#jbntform").submit();
}

function GetJbntValue() {
    var areavalue = $("#JBNTZMJ").html();
    return areavalue;
}

//GeometryHelper.ashx中的后台方法

 if (context.Request.Form["jbnttype"] == "exportjbnt")//导出基本农田表格到excel
            {
                string area = context.Request.Params["jbntarea"];
                string tile = "基本农田保护区面积统计表(公顷)";
                pGeoJson= CommUtility.ExportJbnt2Excel(tile,area);

            }

//创建excel
 public static string ExportJbnt2Excel(string Exceltitle, string area)
        {
            //创建工作薄
            HSSFWorkbook wk = new HSSFWorkbook();
            //创建一个名称为Sheet1的表
            ISheet tb = wk.CreateSheet();
            wk.SetSheetName(,"Sheet1");
            for (int i = ; i < ; i++)
            {
                ICellStyle cellStyle = SetCellStyle(wk, i);
                IRow row = tb.CreateRow(i);
                for (int j = ; j < ; j++)
                {
                    ICell cell = row.CreateCell(j);
                    cell.CellStyle = cellStyle;
                }

            }

            MergeCell(tb, tb.GetRow().GetCell(), , , , , Exceltitle);
            MergeCell(tb, tb.GetRow().GetCell(), , , , , "基本农田占用总面积");
            MergeCell(tb,tb.GetRow().GetCell(),,,,,area);

            MemoryStream mstream = new MemoryStream();
            wk.Write(mstream);
            DownloadFile(mstream, Exceltitle);
            return null;
        }

   //在客户端保存或查看用流生成的excel文件
public static string DownloadFile(MemoryStream fs, string filename)//必须为FileStream或MemoryStream ，如果用Stream则生成的excel无法正常打开{ 
string fileName = filename+".xls";//客户端保存的文件名 //以字符流的形式下载文件 
byte[] bytes = fs.ToArray(); fs.Read(bytes, , bytes.Length); fs.Close(); 
System.Web.HttpContext.Current.Response.Clear(); 

System.Web.HttpContext.Current.Response.ClearContent(); 
System.Web.HttpContext.Current.Response.ClearHeaders(); 
System.Web.HttpContext.Current.Response.ContentType = "application/octet-stream"; 

//通知浏览器下载文件而不是打开  
System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8)); 
System.Web.HttpContext.Current.Response.AddHeader("Content-Transfer-Encoding", "binary"); System.Web.HttpContext.Current.Response.BinaryWrite(bytes);
 System.Web.HttpContext.Current.Response.Flush(); 
System.Web.HttpContext.Current.Response.End();
 return null; }