EXTJS AJAX解析XML数据

public String getAllAreaInfos() {
        try {
            List<Areainfo> list = null;
            if(areaName!=null&&!areaName.equalsIgnoreCase("null")&&areaName.trim().length()>0)
            {
                list = mapInfos.findAllAreaInfos(this.subStringAreaName(areaName));
            }
            else
                list = mapInfos.findAllAreaInfos(null);  

            response.setContentType("text/xml;charset=utf-8");
            response.setCharacterEncoding("utf-8");
            PrintWriter pw = null;
            pw = response.getWriter();
            StringBuffer sb = new StringBuffer();
            sb.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");  

            sb.append("<Items>");
            if(list==null)
            {
                sb.append("<Areainfo>");
                sb.append("<id>").append("no").append("</id>");
                sb.append("</Areainfo>");
            }
            else
            {
                for (int i = 0; i < list.size(); i++)
                {
                    Areainfo v = list.get(i);
                    sb.append("<Areainfo>");  

                    sb.append("<id>").append(v.getId()).append("</id>");
                    sb.append("<name>").append(v.getName()).append("</name>");
                    sb.append("<allCapacity>").append(v.getAllcapacity()).append("</allCapacity>");  

                    sb.append("</Areainfo>");
                }
            }
            sb.append("</Items>");  

            String xmlDBTree = sb.toString();  

            pw.print(xmlDBTree);
            pw.flush();
            pw.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    } 

<?xml version="1.0" encoding="UTF-8"?>"
<Items>
    <Areainfo>
    <id>xxx</id>
    <name>xxxx</name>
    <allCapacity>xxxx</allCapacity>
    </Areainfo>
</Items>

function getAllAreaInfos()
    {
        var areaName = "";
        Ext.Ajax.request({
            method: 'POST',
            url: 'allAreaInfos',
            params: {"areaName":areaName},
            waitMsg: '数据更新中，请稍后...',
            success: function(response,options){
                var xmlDoc = response.responseXML;
                if(xmlDoc!=null)
                {
                    var ais = xmlDoc.getElementsByTagName("Areainfo");
                    if(ais!=null&&ais.length>0)
                    {
                        for(var i=0;i<ais.length;i++)//   DB
                        {
                            var asId = (ais[i].getElementsByTagName("id")[0].childNodes[0].nodeValue);    //  第i个areaInfos的id
                            var asName = (ais[i].getElementsByTagName("name")[0].childNodes[0].nodeValue);    //  第i个areaInfos的名字
                            var allCapacity = (ais[i].getElementsByTagName("allCapacity")[0].childNodes[0].nodeValue);    //  第i个areaInfos的总装机容量
                            //document.getElementById(asName).innerHTML="";
                            document.getElementById(asName).innerHTML=allCapacity;//得到的数据在页面上展示
                        }
                    }
                }
            },
            failure: function(response,options){
                Ext.Msg.alert("信息提示", "获取数据库数据出错,请稍后再试！");
            },
            autoAbort:false
        });
    }