WebApi 只返回Json

    public class JsonContentNegotiator : IContentNegotiator
    {
        private readonly JsonMediaTypeFormatter _jsonFormatter;
        public JsonContentNegotiator(JsonMediaTypeFormatter formatter)
        {
            _jsonFormatter = formatter;
        }
        public ContentNegotiationResult Negotiate(Type type, HttpRequestMessage request, IEnumerable<MediaTypeFormatter> formatters)
        {
            var result = new ContentNegotiationResult(_jsonFormatter, new MediaTypeHeaderValue("application/json"));
            return result;
        }
    }

 protected void Application_Start()
        {
            //只返回json   清除其他所有的formatters 
            GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();
            
            //设置Jsonp格式序列化方法
            GlobalConfiguration.Configuration.Formatters.Insert(0, new JsonpMediaTypeFormatter());

            AreaRegistration.RegisterAllAreas();
            GlobalConfiguration.Configure(WebApiConfig.Register);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
        }

  public static void Register(HttpConfiguration config)
        {
            // Web API 配置和服务
            // 将 Web API 配置为仅使用不记名令牌身份验证。
            //config.SuppressDefaultHostAuthentication();
            //config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

            var jsonFormatter = new JsonMediaTypeFormatter();
            //optional: set serializer settings here            
            config.Services.Replace(typeof(IContentNegotiator), new JsonContentNegotiator(jsonFormatter));

            // Web API 路由
            config.MapHttpAttributeRoutes();

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