从控制台生成的ASP.NET Web Api

using Owin;
using System.Web.Http;

namespace YourConsoleAppProjectNamespace {
    public class Startup {
        public void Configuration(IAppBuilder appBuilder) {
            HttpConfiguration config = new HttpConfiguration();
            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
            appBuilder.UseWebApi(config);
        }
    }
}

修改项目的Main()

using Microsoft.Owin.Hosting;
using System;

namespace YourConsoleAppProjectNamespace {
    class Program {
        static void Main(string[] args) {
            WebApp.Start<Startup>("http://localhost:3333/");
            Console.ReadLine(); // block main thread
        }
    }
}

用动作方法定义控制器并进行测试。