DataTable导出生成Excel文件，并提供下载！

这种方式出来的Excel文件不是Excel工作薄格式，要自己从新另存为一下！

 StringBuilder sb = new StringBuilder();
           
            sb.Append("<table border=1>");

            for (int j = 0; j < dt.Rows.Count;j++)
            {
                sb.Append("<tr>");
                for (int i = 1; i < dt.Columns.Count; i++)
                {
                    sb.AppendFormat("<td>{0}</td>", dt.Rows[j][i].ToString());
                }
                sb.Append("</tr>");
            }
            sb.Append("</table>");

            System.Web.HttpContext curContext = System.Web.HttpContext.Current;

            curContext.Response.ContentType = "application/ vnd.ms-excel";
            curContext.Response.AddHeader("Content-Disposition", "attachment;filename=" + DateTime.Now.ToString("yyyyMMddhhmmss") + ".xls");//这里写地址！现在是自动取的当前时间。
            curContext.Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
            curContext.Response.Charset = "";

            curContext.Response.Write(sb);
            curContext.Response.End();