struts2+Ext 显示网格

我的js代码如下:
/**
 * @author fox
 */
Ext.onReady(function(){
//Ext.BLANK_IMAGE_URL = 'extjs/resources/images/default/s.gif';
//Ext.QuickTips.init();
var sm = new Ext.grid.CheckboxSelectionModel();
var cm = new Ext.grid.ColumnModel([
new Ext.grid.RowNumberer(),
sm,
    {header:'姓名',dataIndex:'stuName',sortable:true},
    {header:'学号',dataIndex:'stuNum',sortable:true},
    {header:'性别',dataIndex:'stuSex',renderer:function(value){
     if(value=='男'){
     return "<span style='color:red;font-weight:bold;'>男</span>";
     }else{
     return "<span style='color:green;font-weight:bold;'>女</span>";
     }
    }}, //增加性别
    {header:'年龄',dataIndex:'stuAge'},
    {header:'电子信箱',dataIndex:'email'}
]);
var store = new Ext.data.Store({
     proxy: new Ext.data.HttpProxy({url:'http://localhost:8000/Student/JsonPlugin.action'}),    
    reader: new Ext.data.JsonReader({root: 'root'}, 
    [
    'stuName','stuNum','stuSex','stuAge','email',
    {name: 'stuName',mapping:'stuName',type:'string'},
    {name: 'stuNum',mapping:'stuNum',type:'string'},
    {name: 'stuSex',mapping:'stuSex',type:'string'},
    {name: 'stuAge',mapping:'stuAge',type:'int'},
    {name: 'email',mapping:'email',type:'string'}
])
});
var grid = new Ext.grid.GridPanel({
    store: store,
    sm: sm,
    cm: cm,
    width:700,
    height:280
});
//el:指定html元素用于显示grid
grid.render('grid');
});我在页面可以显示当前这样的Grid,标题什么都可以显示,就是没有数据显示出来,在红色链接区域http://localhost:8000/Student/JsonPlugin.action 单独测试是完全可以返回JSON数据的,在Ext一结合就不能运行该请求,用debug测试无法进去该方法,请各位帮我解决下,谢谢啦,我也是刚接触,急用.