ext服务器数据交互的一些问题

这是我JS中的部分代码var user = Ext.data.Record.create([
           {name:'userID',type: 'string'},
           {name:'userName',type: 'string'},
           {name:'buMen',type: 'string'}
       ]);
   var store=new Ext.data.Store({
       url:'/AMSWEB/user.do?method=execute', 
       reader: new Ext.data.XmlReader({
           record:'user',
           id: 'userID'
       },user)
       //remoteSort:true    
   });
   store.load({params:{start:0,limit:10}});     var rform = new Ext.form.FormPanel({
       id:'rform',
       header: false,
       frame: true,
       hideBorders: false,
       items: [
       new Ext.form.TextField({
           labelAlign:'center',
           fieldLabel: '用户ID',
           name:'userID'
       }),
       new Ext.Panel({
              layout: 'table',
                buttonAlign: 'center',
                layoutConfig: { colspan: 3 },
               buttons:[{text: '搜  寻',
                  handler: function() {
                        var userID = Ext.get('userID').dom.value;                         
                       store.reload({params:{start:0,limit:3,userID:userID}}); 
                       alert("3");
                      }
               },
               {
                  text: '重  置',
                  handler: function() {
                          Ext.getCmp('rform').form.reset();
                  }
               }
                 ]
           })
          ]
         }); 这是aciton中的代码
以下内容为程序代码:public ActionForward execute(ActionMapping mapping, ActionForm form,
           HttpServletRequest request, HttpServletResponse response)
       throws Exception{
       // TODO Auto-generated method stub
       String user_id=request.getParameter("userID");
       String start=request.getParameter("start");
       String limit=request.getParameter("limit");
       
       System.out.println(user_id+" "+start+" "+limit);
       if(user_id==null || user_id.equals("null")){
           user_id="";
       }
       UserMessageProxy proxy=new UserMessageProxy();
       Collection coll=proxy.getUserMessage(user_id);
       
       PrintWriter out = response.getWriter();
       String s = "";
       s+="<users><user><userID>Tom</userID><userName>Tom</userName><buMen>IT</buMen></user></users>";
       System.out.println(s);       if(coll.size()>0){
           request.setAttribute("result_coll", coll);
       }else{
           System.out.println("查询失败!");
       }
       out.write(s);
       out.flush();
       out.close();
       return null;
   }我跟着例子做，他说s能生成那个与xml文件差不多的东西，在ext用xml 方式读取，为什么我的无法显示，至少会显示s这一条啊，不知道哪里有错，高手告诉我一下，谢谢