1、在WebApiConfig中建立建立HttpControllerHandler和HttpControllerRouteHandler 并覆写它

public class SessionRouteHandler : HttpControllerHandler,IRequiresSessionState        {            public SessionRouteHandler(RouteData routeData)                : base(routeData)            {            }        }        public class SessionControllerRouteHandler : HttpControllerRouteHandler        {            protected override IHttpHandler GetHttpHandler(RequestContext requestContext)            {                return new SessionRouteHandler(requestContext.RouteData);            }        }

Routes.MapHttpRoute要修改为下面的格式：

public static void Register(HttpConfiguration config)        {            RouteTable.Routes.MapHttpRoute(                name: "DefaultApi",                routeTemplate: "api/{controller}/{action}/{id}",                defaults: new { id = RouteParameter.Optional }            ).RouteHandler = new SessionControllerRouteHandler();        }

2、在MVC的WebApi中默认是没有开启Session会话支持的。需要在Global中重写Init方法来指定会话需要支持的类型

public override void Init()        {            PostAuthenticateRequest += MvcApplication_PostAuthenticateRequest;            base.Init();        }        void MvcApplication_PostAuthenticateRequest(object sender, EventArgs e)        {            HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);        }