struts2+ext+json 显示问题

Ext.onReady( function() { var sm = new Ext.grid.CheckboxSelectionModel();
                //设置性别字的样式
            function renderSex(value)
            {
                if ('F' == value) {
                    return "<span style='color:red;font-weight:bold;'>女</span>";
                } else {
                    return "<span style='color:green;font-weight:bold;'>男</span>";
                }
            }      
  /**       var store = new Ext.data.Store({
     proxy: new Ext.data.MemoryProxy(data),
    reader: reader
}); //对应关系，数据和列
       **/    
    var store = new Ext.data.JsonStore({   
       url:'JsonPlugin.action',
      reader : new Ext.data.JsonReader(
{totalProperty : 'totalProperty',root : 'root'}, 
   [            {name: 'id',type : 'int'},
                    {name: 'stuName',type : 'string'},
                    {name: 'stuNum',type : 'string'},
                    {name: 'stuSex',type : 'string'},
                    {name: 'stuAge',type : 'int'},
                    {name: 'email',type : 'string'}
     ])
    });              // create the Grid
            var grid = new Ext.grid.GridPanel({
                store: store,
                columns: [
                    new Ext.grid.RowNumberer() ,
                    sm,
                     {id:'id',header: "主键", width: 150, sortable: true, dataIndex: 'id'},
                    {id:'stuName',header: "学生名", width: 150, sortable: true, dataIndex: 'stuName'},
                    {header: "学号", width: 150, sortable: true, dataIndex: 'stuNum'},
                    {header: "性别", width: 75, sortable: true, dataIndex: 'stuSex',renderer:renderSex},
                    {header: "年龄", width: 75, sortable: true, dataIndex: 'stuAge'},
                    {header: "电子邮箱", width: 205, sortable: true, dataIndex: 'email'}
                ],
                stripeRows: true,
                sm:sm,
                loadMask:true,
                enableColumnMove:true,  //�Ϸ���
                enableColumnResize:true,     //�ı��еĿ��
                height:450,
                width:500,
                title:'学生信息',
                viewConfig:{
                    forceFit:true   
                },
                renderTo: document.body
            });
            store.load();
        
        });我的可以进去'JsonPlugin.action'连接中,但是一直不是很明白 reader : new Ext.data.JsonReader(
{totalProperty : 'totalProperty',root : 'root'}, 这一句是什么意思,我在配置struts.xml文件中: <package name="json" extends="json-default">
<action name="JsonPlugin" class="jsonPluginAction">
<result type="json"/>
</action>
</package>
我看这里有些人的配置是:     <result type="json">
              <param name="root">root</param>
           </result>
在这里的<param name="root">root</param>是必要的嘛?
现在整个demo就是数据无法显示出来,有哪位高人指点下