datagrid 中的内容转换成excel

StringBuilder sbuilder = new StringBuilder();
   StringWriter swriter = new StringWriter(sbuilder);
   HtmlTextWriter htwriter = new HtmlTextWriter(swriter);
   DataGrid1.RenderControl(htwriter);
            StreamWriter swriter1 = File.CreateText(Server.MapPath("G.xls"));

   swriter1.Write(sbuilder.ToString());

   swriter1.Close();