Extの非同期要求(2次カスケード動的ロードドロップダウンリスト)

ページ:

<tr>
			<td class="label" width="300" >       </td>
			<td> 
				<select name="modelId" size="1" style="width: 6.8cm;" id="s1"  subid="s2" onchange="javascript:chooseFunction();">
                           <option value="">   </option>
                 			<%for(int i=0;i<modellist.size();i++){
                 			TawwpModelVO tawwpModelVO = (TawwpModelVO)modellist.get(i);%>
                 			<option value='<%=tawwpModelVO.getId()%>'><%=tawwpModelVO.getModelName()%></option>
                 			<% }%>
                 </select>
			</td>
		</tr>
		<tr>
			<td class="label"  >
			       
			</td>
			<td>	
				<input id="f1" type="hidden"  style="width: 6.8cm;">  
				<select name="functionId" size="1" style="width: 6.8cm;" id="s2" >					
                </select>   
			 </td>
		</tr>	

 
 
フロントページの呼び出し:
フロントがjsonの処理を受信

Ext.Ajax.request({
		method:'post',
               	url: '../assessmodel/functionContent.do?functionId='+id,                           
               	success: function(json){ 
					  var aa = json.responseText;
					  var data = eval('('+aa+')');
					  var bb=data.rows;
					  var sele = document.getElementById("s2");
					  sele.innerHTML = "";
					  var option2 = document.createElement('option');
					  	option2.value ="";
					  	option2.text= "   ";
					  	option2.selected="selected";
					  	sele.add(option2);		
					  for(var i=0;i<bb.length;i++){
					  	var option = document.createElement('option');
					  	option.value = bb[i].id;
					  	option.text= bb[i].name;
					  	sele.add(option);					  	
					  }	 
				},
               failure : function() { 
                      alert("      "); 
        	  } 
           });	

バックグラウンドの処理:

private ActionForward findFunction(ActionMapping mapping, ActionForm form,
			HttpServletRequest request, HttpServletResponse response) {
		IAssessModelMgr assessModelMgr = (IAssessModelMgr) getBean("assessModelMgr");
		String id = request.getParameter("functionId");
		List assList =null;	
		List nList = new ArrayList();
	    
		try {
			assList = assessModelMgr.findFunctionList(id);
			//request.setAttribute("functionList",assList);
			for(int i=0;i<assList.size();i++){
				Map map = new HashMap();
				TawwpModelContentVO  fu = new  TawwpModelContentVO();
				fu=(TawwpModelContentVO)assList.get(i);
				map.put("id", fu.getContendid());
				map.put("name",fu.getName());
				nList.add(map);
			}
			response.setContentType("text/xml;charset=UTF-8");

			//   JSON  
			response.getWriter().print(JSONUtil.list2JSON(nList));
			return null;			
		} catch (Exception e) {
			//generalError(request, e);
			ActionMessages messages = new ActionMessages();
			messages.add(ActionMessages.GLOBAL_MESSAGE, new ActionMessage(
					"submit.title.failure"));
			saveMessages(request, messages);
			return mapping.findForward("failure");
		}		
	}