ajax发送数据时。在struts2action中获取不到


这是后台action类
public class listActioncity extends ActionSupport {
citydao cdao=new citydao();
JSONArray jsonarray;


public String execute(){
HttpServletResponse resp=ServletActionContext.getResponse();
resp.setCharacterEncoding("utf-8");
HttpServletRequest req=ServletActionContext.getRequest();
String provinceid=req.getParameter("pid");

System.out.println(provinceid);

List<City> list=cdao.citylist(1);
jsonarray=JSONArray.fromObject(list);
try {
System.out.println(jsonarray.toString());
resp.getWriter().write(jsonarray.toString());
resp.getWriter().flush();
resp.getWriter().close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return SUCCESS;
} public JSONArray getJsonarray() {
return jsonarray;
} public void setJsonarray(JSONArray jsonarray) {
this.jsonarray = jsonarray;
}

}这是jsp页面 var citys={pid:'1'};
              params={city:citys};

$.ajax({
type:"post",
url:"listActioncity.action",
dataType:"json",
data:{pid:'2'},
success:callback

});

function callback(data){
var city1=eval("("+data+")");
alert(city1)

}
/*$.post("listActioncity.action",{pid:2},function(data){
var city1=eval("("+data+")");
alert(city1)
 这是struts.xml：
<package name="default" extends="json-default">
<action name="listActioncity" class="action.listActioncity" >
<result type="json">
<param name="root">jsonarray</param>
</result>
</action>