jfinal结合ajax

$.ajax({
type: "post",
dataType: 'json',
url: '/checkCity',
data: {cityname: $('#autocomplete').val()},
success:function(res){
if(res.err == 0) {
window.location.href = '/'+res.cityname;
} else {
alert('对不起，该城市不存在!')
}
}
});

//加入Controller
add("/checkCity", CheckCityController.class);

//Controller写方法，返回参数
public class CheckCityController extends Controller {

public void index() {
String cityname = getPara("cityname");
ArrayList<String> cities = City.getAllCities();
if (cities.contains(cityname)) {
setAttr("err", 0);
setAttr("cityname", cityname);
} else {
setAttr("err", 1);
}
renderJson();
}

}