asp.net mvc让api返回json格式

ASP.NET Web API的controller默认的返回数据格式是XML格式,要改成返回JSON格式只需要在WebApiConfig.cs文件里的Register方法末尾加上如下代码

var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);

WebApiConfig.cs 完整代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Http;

namespace HaoSiJiaWeb
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API 配置和服务

            // Web API 路由
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
              name: "DefaultApi",
              routeTemplate: "api/{controller}/{id}",
              defaults: new { id = RouteParameter.Optional }
          );

            config.Routes.MapHttpRoute(
            name: "DefaultApi2",
            routeTemplate: "api/{controller}/{action}/{id}",
            defaults: new { id = RouteParameter.Optional }
            );

            config.Routes.MapHttpRoute(
            name: "DefaultApi3",
            routeTemplate: "api2/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional },
            constraints:new { id = @"\d*" }
            );

            var json = config.Formatters.JsonFormatter;
            json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
            config.Formatters.Remove(config.Formatters.XmlFormatter);
        }
    }
}

参考：http://blchen.com/change-asp-net-web-api-default-return-type-to-json/