GlobalConfiguration.Configuration.Formatters.JsonFormatter.MediaTypeMappings.Add(new QueryStringMapping("json", "true", "application/json"));

 1 protected void Application_Start()
 2 {
 3     AreaRegistration.RegisterAllAreas();
 4     //添加json 解析  使用方法 http://xxx/api/action?json=true
 5     GlobalConfiguration.Configuration.Formatters.JsonFormatter.MediaTypeMappings.Add(new QueryStringMapping("json", "true", "application/json"));
 6     WebApiConfig.Register(GlobalConfiguration.Configuration);
 7     FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
 8     RouteConfig.RegisterRoutes(RouteTable.Routes);
 9     BundleConfig.RegisterBundles(BundleTable.Bundles);
10 }

GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();

 1 protected void Application_Start()
 2 {
 3     AreaRegistration.RegisterAllAreas();
 4     WebApiConfig.Register(GlobalConfiguration.Configuration);
 5     FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
 6     RouteConfig.RegisterRoutes(RouteTable.Routes);
 7     BundleConfig.RegisterBundles(BundleTable.Bundles);
 8     //删除xml的解析 当返回值是string 时 直接返回string不是json对象
 9     GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear(); 
10 }

 1 新建方法 需要程序集：System.Web.Extensions
 2 public static HttpResponseMessage ToJson(Object obj)
 3 {
 4     String str;
 5     if (obj is String || obj is Char)
 6     {
 7         str = obj.ToString();
 8     }
 9     else
10     {
11         var serializer = new JavaScriptSerializer();
12         str = serializer.Serialize(obj);
13     }
14     var result = new HttpResponseMessage { Content = new StringContent(str, Encoding.GetEncoding("UTF-8"), "application/json") };
15     return result;
16 }

1 public HttpResponseMessage GetString(string name)
2 {
3     return ToJson(name);
4 }

 1 新建JsonContentNegotiator 类
 2 public class JsonContentNegotiator : IContentNegotiator
 3 {
 4     private readonly JsonMediaTypeFormatter _jsonFormatter;
 5     public JsonContentNegotiator(JsonMediaTypeFormatter formatter)
 6     {
 7         _jsonFormatter = formatter;
 8     }
 9 
10     public ContentNegotiationResult Negotiate(Type type, HttpRequestMessage request, IEnumerable<MediaTypeFormatter> formatters)
11     {
12         var result = new ContentNegotiationResult(_jsonFormatter, new MediaTypeHeaderValue("application/json"));
13         return result;
14     }
15 }

 1 WebApiConfig中使用重写
 2 public static void Register(HttpConfiguration config)
 3 {
 4     config.Routes.MapHttpRoute(
 5         name: "DefaultApi",
 6         routeTemplate: "api/{controller}/{id}",
 7         defaults: new { id = RouteParameter.Optional }
 8     );
 9 
10     var jsonFormatter = new JsonMediaTypeFormatter();
11     config.Services.Replace(typeof(IContentNegotiator), new JsonContentNegotiator(jsonFormatter));
12 
13     // 取消注释下面的代码行可对具有 IQueryable 或 IQueryable<T> 返回类型的操作启用查询支持。
14     // 若要避免处理意外查询或恶意查询，请使用 QueryableAttribute 上的验证设置来验证传入查询。
15     // 有关详细信息，请访问 http://go.microsoft.com/fwlink/?LinkId=279712。
16     //config.EnableQuerySupport();
17 
18     // 若要在应用程序中禁用跟踪，请注释掉或删除以下代码行
19     // 有关详细信息，请参阅: http://www.asp.net/web-api
20     config.EnableSystemDiagnosticsTracing();
21 }