ajax回调函数中如何获取action中的数据

//action 中 

HttpServletResponse response = ServletActionContext.getResponse(); 

response.setContentType("text/plain;charset=UTF-8"); 

try { 
     response.getWriter().write("Hello"); 
} catch (IOException e) { 
e.printStackTrace(); 
} 
return null; 

ajax：

$.ajax({ 
   type: "POST", 
   url: "请求action路径", 
   data: "提交参数", 
   success: function(data){ 
     alert(data);//返回数据date
   } 
});

页面弹出“Hello”