private void Export(int pageIndex = 0)
        {
            var sb = new StringBuilder();
            。。。
            Response.Clear();
            Response.Buffer = true;
            Response.Charset = "UTF-8";
            Response.Write("<meta http-equiv=Content-Type content=text/html;charset=UTF-8>");
            Response.AppendHeader("Content-Disposition", "attachment;filename=" +
                            HttpUtility.UrlEncode(fileName + ".html", Encoding.UTF8).ToString());
            Response.ContentEncoding = System.Text.Encoding.GetEncoding("UTF-8");
            Response.ContentType = "text/html";
            Response.Write(sb.ToString());
            Response.Flush();
            Response.End();
        }