easyui+jsp+serlet返回数据页面显示的问题

Question

$(function(){
$('#tt').datagrid({
title:'datagrid小例子',
iconCls:'icon-ok',
width:500,
height:320,
nowrap:false,
striped: true,
collapsible:true,
url:'StudentAction',
loadMsg:'数据装载中......',
sortName:'code',
sortOrder:'desc',
remoteSort:false,
frozenColumns:[[
{field:'ck',checkbox:true}
]],
columns:[[
{title:'学号',field:'id',width:'140',rowspan:2,align:'center'},
{title:'姓名',field:'name',width:'150',rowspan:2,align:'center'},
{title:'班级',field:'className',width:'150',rowspan:2,align:'center'}
]],
pagination:true,
rownumbers:true

});
$('#tt').datagrid('getPager').pagination({displayMsg:'当前显示从{from}到{to}共{total}记录'});
});

public class StudentAction extends HttpServlet {

private static final long serialVersionUID = 1L;
private static int Num = 10;
private int total;
private List<Object> rows;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("welcome to studentAction");
      this.total = 100;
      this.rows = new ArrayList<Object>();
      for(int i=0;i<Num;i++){
       Student student = new Student();
       student.setId("id_"+i);
       student.setName("name_"+i);
       student.setClassName("className_"+i);

       Map<String,Object> map = new HashMap<String,Object>();
       map.put("id", student.getId());
       map.put("name", student.getName());
       map.put("className",student.getClassName());

       this.rows.add(map);


      }