jquery-ajax、struts2、json数据问题

jquery代码：

 $.ajax({
    url:url,
    type:'post',
    data:{"key1": "value1", "key2": "value2"},
    dataType:'json',
    error:function(){},
    success:function(result){
      $("#id").html(result.key1);
    }
  });

java代码：

 public String testAjax(){

   response.setContentType("application/x-json");
   response.setCharacterEncoding("UTF-8");

   String value1 = request.getParameter("key1");
   String value2 = request.getParameter("key2");
   String value3 = request.getParameter("key3");

   Map<String, Object> map = new HashMap<String, Object>();
   map.put("key1", value1);
   map.put("key2", value2);
   map.put("key3", value3);

   PrintWriter out = null;
   try{
     out.response.getWriter();
     //将map转换成json格式，具体用法及所需jar包可以参考官方文档
     JSONObject result = JSONObject.fromObject(map);
     out.print(result);
     out.flush();
   }catch(IOException e){
     e.printStackTrace();
   }finally{
     if(out != null){
       out.close();
     }
   }
   return null;
 }