Web API 返回json文件的2中不用方式

  //方法一：直接返回序列化后的json文件
        public static HttpResponseMessage ConvertToJson(this Object obj)
        {

            String str="";
            if (obj is String || obj is Char)
            {
                str = obj.ToString();
            }
            else
            {
                string json = Newtonsoft.Json.JsonConvert.SerializeObject(obj);
            }
            HttpResponseMessage result = new HttpResponseMessage { Content = new StringContent(str, Encoding.GetEncoding("UTF-8"), "application/json") };
            return result;
        }

   //方法二：global.asax.cs文件中加上
    HttpResponseMessage result = new HttpResponseMessage { Content = new StringContent(str, Encoding.GetEncoding("UTF-8"), "application/json") };