extjs 的gridPanel通过JsonStore取不到值

这是显示部分
var store=new Ext.data.JsonStore({
              
    proxy: new Ext.data.HttpProxy({
     url: 'getUserData.jsp'
    }),
   
    //url:'http://design/getUserData.jsp',

    reader: new Ext.data.JsonReader(
     {fields:['username','usergroup']}
    )
               /* fields:[
                    {name:'username'},
                    {name:'usergroup'}]
               */
            });

            store.load();
         

            var gridPanel=new Ext.grid.GridPanel({
                store:store,
                columns:[
                    /*{
                        header:'用户ID',
                        dataIndex:'id',
                        width:100
                    },*/
                    {
                        header:'用户名',
                        dataIndex:'username',
                        width:160
                    },{
                        header:'用户组',
                        dataIndex:'usergroup',
                        width:160
                    }],
                viewConfig:{
                    sortAscText:'正序排列',
                    sortDescText:'逆序排列',
                    forceFit:true
                },
                width:600,
                height:400,

                frame:true,
                //title:'Framed with Checkbox Selection and Horizontal Scrolling',
                iconCls:'icon-grid'
            });
下面是数据，读取的页面的内容没有html,head和body标签，只有
[
{"username":"aaa","usergroup":"bbb"},
{"username":"bbb","usergroup":"111"}
]

我试过直接在store用data属性直接给值，显示正常，但是一旦到网页去取，就取不到值
现在死活拿不到值，试过很多方法了