让web api 4.5支持Jquery.getJson(url,handle)跨域访问

代码片段，google了半天，找到的都是4.5 rc，或之前版本的代码，发现都不能用，正式版后有些方法做了修改。我重新修改一下分享给大家

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public static class HttpRequestMessageExtensions

    {

        public static string QueryString(this HttpRequestMessage request, string name)

        {

            string requestUri = request.RequestUri.Query;

            string[] queries = requestUri.Split('&');

 

            foreach (string s in queries)

            {

                if (s.Contains(name))

                {

                    int index = s.IndexOf('=');

                    int stopIndex = s.IndexOf('&', index);

                    if (stopIndex != -1)

                        return s.Substring(index + 1, stopIndex - index - 1);

                    else

                        return s.Substring(index + 1, s.Length - index - 1);

                }

            }

 

            return string.Empty;

        }

    }

    public class JsonpMediaTypeFormatter : JsonMediaTypeFormatter

    {

        private string callbackQueryParameter;

        private HttpRequestMessage httpRequest;

        public JsonpMediaTypeFormatter()

        {

            SupportedMediaTypes.Add(DefaultMediaType);

            SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/javascript"));

 

            MediaTypeMappings.Add(new UriPathExtensionMapping("jsonp", DefaultMediaType));

        }

 

        public string CallbackQueryParameter

        {

            get { return callbackQueryParameter ?? "callback"; }

            set { callbackQueryParameter = value; }

        }

        public override MediaTypeFormatter GetPerRequestFormatterInstance(Type type, HttpRequestMessage request, MediaTypeHeaderValue mediaType)

        {

            httpRequest = request;

            return base.GetPerRequestFormatterInstance(type, request, mediaType);

        }

        public override Task WriteToStreamAsync(

              Type type, object value, Stream stream, HttpContent content, TransportContext transportContext)

        {

            string callback;

 

            if (IsJsonpRequest(out callback))

            {

                return Task.Factory.StartNew(() =>

                {

                    var writer = new StreamWriter(stream);

                    writer.Write(callback + "(");

                    writer.Flush();

 

                    base.WriteToStreamAsync(type, value, stream,content, transportContext).Wait();

 

                    writer.Write(")");

                    writer.Flush();

                });

            }

            else

            {

                return base.WriteToStreamAsync(type, value, stream, content, transportContext);

            }

        }

 

 

        private bool IsJsonpRequest(out string callback)

        {

            callback = null;

 

            //if (HttpContext.Current.Request.HttpMethod != "GET")

            if(httpRequest.Method!=HttpMethod.Get)

                return false;

            //var uri = httpRequest.RequestUri;

            //var query = uri.Query;

            callback = httpRequest.QueryString(CallbackQueryParameter);

 

            return !string.IsNullOrEmpty(callback);

        }

    }

　　

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var config = new HttpSelfHostConfiguration(baseAddress);

     

               // Set the max message size to 1M instead of the default size of 64k and also

               // set the transfer mode to 'streamed' so that don't allocate a 1M buffer but

               // rather just have a small read buffer.

               config.MaxReceivedMessageSize = 1024 * 1024;

               config.TransferMode = TransferMode.Streamed;

               config.Formatters.Insert(0, new JsonpMediaTypeFormatter());

　　

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$('#getjson').bind('click', function () {

            $.getJSON("http://192.168.103.135:8080/api/products/1?jsoncallback=?",

                function (data) {

                    $("#result").append(data);

                    return;

                    $("#result").append(data.Image);

                    $("<img/>").attr("src", "data:image/jpeg;base64," + data.Image).appendTo("#result");

                    return;

                    $.each(data, function (i, item) {

                        $("#result").append(item.Name);

                        $("<img/>").attr("src", item.Image).appendTo("#result");

 

                    });

                });

        });