webapi之jsonp调用

定义跨域handle

    public class CorsHandler : DelegatingHandler
    {
        const string Origin = "Origin"; const string AccessControlRequestMethod = "Access-Control-Request-Method"; const string AccessControlRequestHeaders = "Access-Control-Request-Headers"; const string AccessControlAllowOrigin = "Access-Control-Allow-Origin"; const string AccessControlAllowMethods = "Access-Control-Allow-Methods"; const string AccessControlAllowHeaders = "Access-Control-Allow-Headers";
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            bool isCorsRequest = request.Headers.Contains(Origin); bool isPreflightRequest = request.Method == HttpMethod.Options; if (isCorsRequest)
            {
                if (isPreflightRequest)
                {
                    return Task.Factory.StartNew<HttpResponseMessage>(() =>
                    {
                        HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
                        response.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First()); string accessControlRequestMethod = request.Headers.GetValues(AccessControlRequestMethod).FirstOrDefault(); if (accessControlRequestMethod != null)
                        {
                            response.Headers.Add(AccessControlAllowMethods, accessControlRequestMethod);
                        } string requestedHeaders = string.Join(", ", request.Headers.GetValues(AccessControlRequestHeaders)); if (!string.IsNullOrEmpty(requestedHeaders))
                        {
                            response.Headers.Add(AccessControlAllowHeaders, requestedHeaders);
                        } return response;
                    }, cancellationToken);
                }
                else
                {
                    return base.SendAsync(request, cancellationToken).ContinueWith<HttpResponseMessage>(t =>
                    {
                        HttpResponseMessage resp = t.Result;
                        resp.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First()); return resp;
                    });
                }
            }
            else
            {
                return base.SendAsync(request, cancellationToken);
            }
        }
    }

在Global.asax注册handler

        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            GlobalConfiguration.Configuration.MessageHandlers.Add(new CorsHandler());
            WebApiConfig.Register(GlobalConfiguration.Configuration);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
        }

webapi写法

        public string Get(int id)
        {
            var callback = HttpContext.Current.Request["callback"];
            var u = new User { Name = "AA", Age = id };
            var result = new JavaScriptSerializer().Serialize(u);
            if (string.IsNullOrWhiteSpace(callback))
                return result;            
            return string.Format("{0}({1})", callback, result);
        }

前台写法

                $.ajax({
                    type: "get",
                    url: "http://localhost:21931/api/myapi/12311111",
                    contentType: "application/json;",
                    success: function (msg) {
                        jalert(JSON.stringify(msg));
                    },
                    error: function (a, b, c) {
                        jalert("error");
                    }
                });