function postJson(){
    var json = {"username" : "imp", "password" : "123456"};
    $.ajax({
        type : "post",
        url : "<%=basePath %>ajaxRequest",
        contentType : "application/json;charset=utf-8",
        dataType : "json",
        data: JSON.stringify(json),
        success : function(data){
            alert("username："+data.username+"   id："+data.id);
        },
        error : function(){
            alert("请求失败");
        }
    })
}

<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

    @ResponseBody
    @RequestMapping(value="/ajaxRequest",method=RequestMethod.POST)
    public User ajaxRequest(@RequestBody User user){
        System.out.println(user);
        return user;
    }