SpringBind对象到页面时，用ajax提交form表单内容，后台无法获取绑定对象问题

1.前段页面绑定

<form method="post" class="form-horizontal" >
	#springBind("user.*")
	<input id="id" name="id"  value="$!user.id" type="hidden"/>
	<input id="image" name="image"  value="$!user.image" type="hidden"/>
	<div class="form-group">
                <label class="col-sm-5 control-label"></label>

                 <div class="col-sm-7" style="cursor:pointer;">
			<input id="icon" type="file" style="opacity:0;cursor:pointer;"/>
                       <img style="width:200ox;height:200px;border-radius:100px;" id="user-icon">
                  </div>
       </div>
       <div class="hr-line-dashed"></div>
</form>

2.后台获取对象

public  @ResponseBody String saveOrUpdateUser(HttpServletRequest request, HttpServletResponse response, Model model,@ModelAttribute("user") User user)

3.ajax请求提交form表单

$.ajax({
		type : "POST",
		async : false,
		data : $("form").serialize(),
		url : "saveOrUpdateUser.do",
		dataType : "json",
                contentType:"charset=utf-8"
		success:function(resp){
			if(resp.code == 0){
				layer.msg("保存成功", {icon: 1});
			}else{
				layer.msg("修改失败", {icon: 0});
			}
		},
		error:function(){
			layer.msg("服务器异常", {icon: 0});
		}
	});

但后台获取的user为空，原因在ajax中设置的contentType:"charset=utf-8",将这行去掉就可以接收到对象了