gridpanel无法显示数据

js:
Ext.require(['*']);
Ext.onReady(function(){
var proxy=new Ext.data.HttpProxy({url:'findTeacherNotice',method:'GET'});
//定义reader
var reader=new Ext.data.JsonReader({ root:'items' },
[
{
name : 'noticeTitle',
type : 'string',
maping : 'noticeTitle'
}, {
name : 'noticeTime',
type : 'date',
maping : 'noticeTime'
}, {
name : 'endTime',
type : 'date',
maping : 'endTime'
}
]
)
//构建Store
var store=new Ext.data.Store( {
proxy:proxy,
reader:reader,
autoLoad:true
});
//载入
store.reload();
// create the grid
var grid = new Ext.grid.GridPanel({
store: store,
columns:[
{header:"通知标题", dataIndex:"noticeTitle"},
{header:"通知时间", dataIndex:"noticeTime"},
{header:"有效日期", dataIndex:"endTime"}
],
renderTo:'noticeList',
width:540,
height:200
});
});
json:{"items":[{"endTime":"2014-05-28T00:00:00","id":1,"noticeText":"关于学生防火安全","noticeTime":"2014-05-23T00:00:00","noticeTitle":"防火安全通知","teacher":{"department":"计算机科学与技术系","grade":2011,"password":"123456","phoneNumber":"13647387463","sex":"女","tname":"崔磊","tno":"0420110321"}}],"results":1}