spring 3 mvc json的输出和 jquery ajax的二级联动

在control层数据转换成json对象的代码以下：

@RequestMapping("/getMyPlan")
public @ResponseBody Map
getMyPlan(Integer idKey)throws Exception{
Map josnMap = new
HashMap();
List tasks =
projectManagementService.findTaskByProjectId(idKey);
List
list=new
ArrayList();
if(tasks.size()>0){
for(Task
task:tasks)
{
Map taskMap=new
HashMap();
taskMap.put("id",
task.getId());
taskMap.put("specification",
task.getSpecification());
list.add(taskMap);
}
}
else{
Map
taskMap=new HashMap();
taskMap.put("id",
0);
taskMap.put("specification",
null);
list.add(taskMap);
}
josnMap.put("tasks",list);
return
josnMap;
}

前端的js中ajax的代码以下：

$(function()
{
//ajax给活动计划赋值------------------------------------------------------

$("#activity_project").change(function(){

var pro=$("#activity_project").val();

$.ajax({
type:
"POST",
url:
"${pageContext.request.contextPath}/getMyPlan",

data: { //发送给数据库的数据

idKey:pro

},

dataType: 'json',
success:
function(data) {

$.each(data.tasks,
function(index,item){


$("#activity_taskid").empty();


$("#activity_taskid").append('

'+item.specification+'')

});

}
})

});

//-------------------------------------结束------------------------------------
});