Ajax发送同步请求给Spring，通过controller处理完成后如何返回响应

	@RequestMapping("changeState")
	public String changeState(HttpServletRequest req){
		System.out.println(req.getParameter("status"));
		String status = req.getParameter("status");
		int id = Integer.parseInt(req.getParameter("id"));
		Map<String,Object> map = new HashMap<String,Object>();
		if("0".equals(status)){
			map.put("status","1");
			map.put("id",id);
			costDao.stateChange(map);
		}else{
			map.put("status","0");
			map.put("id",id);
			costDao.stateChange(map);
		}
		return null;
	}

Controller返回值如何填写？？

以下是通过Ajax发送的同步请求

function startFee(status,id) {
                var r = window.confirm("确定要启用此资费吗？资费启用后将不能修改和删除。");
                if(r){
                	var xhr = getXhr();
                	xhr.open("get","changeState.do?status="+status+"&id="+id,false);
                	xhr.onreadystatechange=function(){
                		if((xhr.readyState==4)&&(xhr.status==200)){
                		alert("4");
                		}
                	};
                	xhr.send();
                }
                document.getElementById("operate_result_info").style.display = "block";
            }

解决办法：使用PrintWrite写一个返回值，并且该Controller声明为void