如何让WebServer返回指定XML内容

/*menulist 类开始*/

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml;
using Singcn.SQL;
using System.Data.SqlClient;
using System.IO;
using System.Text;

namespace myfunc.Common
{
/// <summary>
/// PubFunc 的摘要说明
/// </summary>
public class menulist
{
public XmlWriterSettings settings = new XmlWriterSettings();
public XmlWriter writer = null;
public string buf = "";
public SqlShell objShell;
public SqlCommand objCommand;
public DataTable objDataTable;

public menulist(string userid)
{
objShell = new SqlShell();
objCommand = new SqlCommand("select * from qxdmb order by jb,px,qxdm");
objCommand.CommandType = CommandType.Text;
objDataTable = objShell.executeDataSet(ref objCommand).Tables[0];

StringWriter writerstr = new StringWriter();
settings.Indent = true;
settings.Encoding = Encoding.GetEncoding("utf-8");
try
{
writer = XmlWriter.Create(writerstr, settings);

writer.WriteStartDocument();
writer.WriteStartElement("DSTreeRoot");
writer.WriteAttributeString("text", "后台治理系统-[" userid "]");
writer.WriteAttributeString("treeId", "0000");
writer.WriteAttributeString("open", "true");


readqxdmb("0");

writer.WriteEndElement();
writer.WriteEndDocument();
}
finally
{
if (writer != null)
writer.Close();
}
buf = writerstr.ToString();
buf = buf.Replace(@"encoding=""utf-16""", @"encoding=""utf-8""");//在使用StringWriter 作为xml输出时XML自动为“utf-16”，此处用Replace方法处理，如有更好的方法请指教！