owin 返回json字符串多带了双引号"多了重string转义字符串解决办法

 [HttpGet]
        public HttpResponseMessage getsystemtime()
        {
            cltime time = new cltime();
            time.datetime = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");
            string relsut = JsonConvert.SerializeObject(time);
            var resp = new HttpResponseMessage { Content = new StringContent(relsut, System.Text.Encoding.UTF8, "application/json") };
            return resp;

        }

必须HttpResponseMessage 这个返回类型才不会出现