在 WebApiConfig 類中增加方法ConfigureApi，並在 Register 方法最後呼叫一下    ConfigureApi(config);    

增加一個實現IContentNegotiator 介面的類 JsonContentNegotiator

詳細如下：

 public static void ConfigureApi(HttpConfiguration config)

        {
            var jsonFormatter = new JsonMediaTypeFormatter();
            var settings = jsonFormatter.SerializerSettings;

            IsoDateTimeConverter timeConverter = new IsoDateTimeConverter();
            //這裡使用自定義日期格式
            timeConverter.DateTimeFormat = "yyyy'-'MM'-'dd' 'HH':'mm':'ss";
            settings.Converters.Add(timeConverter);


            settings.ContractResolver = new CamelCasePropertyNamesContractResolver();
            config.Services.Replace(typeof(IContentNegotiator), new JsonContentNegotiator(jsonFormatter));   

        }

  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;
        }
    }