Struts2+EXTJS+JSON为什么我得到的值不显示？

最近做ExtJS，遇到一个问题，就是我发送请求可以返回字符串，但是我的前台却显示不出来，也不报错，请大家帮我看看是怎么回事，先谢谢了。这个是我的Action类关键代码： @Override
public String execute() throws Exception {
// TODO Auto-generated method stub
System.out.println("获取到请求");
String msg = ExtHelper.getJsonFromList(manager.search());
System.out.println("msg:"+msg);
ServletActionContext.getResponse().getWriter().write(msg);
return null;
}
下面是我工具类，封装Json数据的代码： /**
 * 将List集合解析成JSON数据
 * @param list
 * @return
 */
public static String getJsonFromList(List list){
TotalJson totalJson = new TotalJson();
totalJson.setItems(list);
totalJson.setTotal(list.size());
JSONObject object = JSONObject.fromObject(totalJson);
return object.toString();
}
封装后的Json数据是这个样子：
{"items":[{"address":"1","id":1,"name":"1"},{"address":"2","id":2,"name":"2"},{"address":"3","id":3,"name":"3"},{"address":"4","id":4,"name":"4"},{"address":"5","id":5,"name":"5"},{"address":"6","id":6,"name":"6"},{"address":"7","id":7,"name":"7"},{"address":"8","id":8,"name":"8"},{"address":"9","id":9,"name":"9"}],"total":9}下面是前台页面代码：Ext.onReady(function(){
            
var store = new Ext.data.Store({
        autoLoad: true,

        proxy: new Ext.data.ScriptTagProxy({
            url: 'student'
        }),

        reader: new Ext.data.JsonReader({
            root: 'items',
            totalProperty: 'total',
            idProperty: 'id',
            fields: [
                {name:'id'},
                {name: 'name'},
                {name: 'address'}
            ]
        })
    });

    var grid = new Ext.grid.GridPanel({
        renderTo: 'grid-div',
        width:700,
        height:600,
        frame:true,
        stripeRows:true,
        title:'<center>***管理</center>',
        store: store,

        columns: [new Ext.grid.RowNumberer({width: 30}),{
            id: 'id',
            header: "编号",
            dataIndex: 'id',
            width: 420,
            sortable:true
        },{
            header: "姓名",
            dataIndex: 'name',
            width: 70,
            align: 'right',
            sortable:true
        },{
            id: 'address',
            header: "地址",
            dataIndex: 'adress',
            width: 150,
            sortable:true
        }],

    bbar: new Ext.PagingToolbar({
    store: store,
    pageSize:20,
    displayInfo:true
    })
    });



});调试出来之后，也不报错，什么也不显示，请各位大哥帮我看看这是什么原因.