如何根据combo的数据，使得GridPanl加载不同的数据（后台数据加载错误）

[size=large]目前的问题是前台不管如何选择combo数据，尽管参数已经传给后台，但是后台总是返回 else 里面的数据，没有执行判断语句。[size=medium][/size]
希望大家看看，错在哪里。谢谢~[/size][code="java"]
/***********************************前台代码****************************************/

Ext.onReady(function()
{
Ext.QuickTips.init();

var proxy=new Ext.data.HttpProxy({url:'ExtCombodata.jsp'});

var MyRecord = Ext.data.Record.create([
                {name: 'id'},
                {name: 'name'},
                {name: 'occupation'}
            ]);

var readergrid=new Ext.data.JsonReader({
    totalProperty: "results",                   //totalRecords属性由json.results得到
    root: "rows",                               //构造元数据的数组由json.rows得到
    id: "id"                                    //id由json.id得到
    },MyRecord
)

//构建Store

var storegrid=new Ext.data.Store({
proxy:proxy,
reader:readergrid,
remoteSort : true,
baseParams : {
jsonData : '11'
}
});
storegrid.reader = '';
// storegrid.load();

var grid = new Ext.grid.GridPanel({
    title:"1111111111",
    height:300,
    width:250,
     columns: [
        {id:'ids',header: "id", width: 20, sortable: true, dataIndex: 'id'},
        {header: "name", width: 75, sortable: true, dataIndex: 'name'},
        {header: "occupation", width: 75, sortable: true, dataIndex: 'occupation'}
    ],
    store:storegrid,
    autoExpandColumn:2
});


var arr=[ [1, 'AAA'], [2, 'BBB'],[3, 'CCC'] ];
var reader = new Ext.data.ArrayReader({id: 0},[{name: 'value'},{name: 'key'}]);

var store=new Ext.data.Store({
  reader:reader

});
store.loadData(arr);
var combo= new Ext.form.ComboBox({
labelStyle: "text-align: 'right';",
fieldLabel:'各个子系统',
editable:false,
triggerAction: 'all',
displayField:'key',
mode: 'local',
store:store ,
listeners:{
select:function(combo, record,index){

                alert('Data: '+combo.getValue());

                storegrid.reader = readergrid;

                if(combo.getValue()=='AAA'){       //这里通过combo的不同选项，向后台传不同的参数
                    storegrid.baseParams.jsonData = "11";
                }else if(combo.getValue()=='BBB'){
                    storegrid.baseParams.jsonData = "22";
                }else{
                    storegrid.baseParams.jsonData = "33";
                }

                storegrid.load();
            }
            }
        });

var panelIE=new Ext.FormPanel({
labelWidth: 50,
labelAlign:'center',
frame:true,
width: 300,
height: 400,
defaultType: 'textfield',
renderTo:'div01',
items:[
new Ext.Panel({}),
combo,
grid

]});
})
/***********************************后台代码（ExtCombodata.jsp）*******************************/
<%@ page language="java" contentType="text/html; charset=GB2312"
pageEncoding="GB2312"%>

<%
String aa= request.getParameter("jsonData");

String tempStr="";

// response.getWriter().write(aa);

if(aa=="11"){
        tempStr="{ 'results': 3, 'rows': [{ 'id': '1', 'name': 'Bill111', 'occupation': 'Gardener' },{ 'id': '11', 'name': 'Ben', 'occupation': 'Horticulturalist' },{ 'id': '111', 'name': 'Bill', 'occupation': 'Horticulturalist' } ]}";

}else if(aa=="22"){
        tempStr="{ 'results': 3, 'rows': [{ 'id': '2', 'name': 'Bill111', 'occupation': 'Gardener' },{ 'id': '22', 'name': 'Ben', 'occupation': 'Horticulturalist' },{ 'id': '222', 'name': 'Bill', 'occupation': 'Horticulturalist' } ]}";

}else{
        tempStr="{ 'results': 3, 'rows': [{ 'id': '3', 'name': 'Bill111', 'occupation': 'Gardener' },{ 'id': '33', 'name': 'Ben', 'occupation': 'Horticulturalist' },{ 'id': '333', 'name': 'Bill', 'occupation': 'Horticulturalist' } ]}"; 

}

response.getWriter().write(tempStr);

%>

[/code]