public static class HttpRequestMessageExtensions
    {
        /// <summary>
        /// Gets the <see cref="HttpConfiguration"/> for the given request.
        /// </summary>
        /// <param name="request">The HTTP request.</param>
        /// <returns>The <see cref="HttpConfiguration"/>.</returns>
        public static HttpConfiguration GetConfiguration(this HttpRequestMessage request)
        {
            if (request == null)
            {
                throw new ArgumentException("request");
            }

            return request.GetProperty<HttpConfiguration>(HttpPropertyKeys.HttpConfigurationKey);
        }

        /// <summary>
        /// Gets the <see cref="System.Threading.SynchronizationContext"/> for the given request or null if not available.
        /// </summary>
        /// <param name="request">The HTTP request.</param>
        /// <returns>The <see cref="System.Threading.SynchronizationContext"/> or null.</returns>
        public static SynchronizationContext GetSynchronizationContext(this HttpRequestMessage request)
        {
            if (request == null)
            {
                throw new ArgumentException("request");
            }

            return request.GetProperty<SynchronizationContext>(HttpPropertyKeys.SynchronizationContextKey);
        }

        /// <summary>
        /// Gets the <see cref="System.Web.Http.Routing.IHttpRouteData"/> for the given request or null if not available.
        /// </summary>
        /// <param name="request">The HTTP request.</param>
        /// <returns>The <see cref="System.Web.Http.Routing.IHttpRouteData"/> or null.</returns>
        public static IHttpRouteData GetRouteData(this HttpRequestMessage request)
        {
            if (request == null)
            {
                throw new ArgumentException("request");
            }

            return request.GetProperty<IHttpRouteData>(HttpPropertyKeys.HttpRouteDataKey);
        }

        public static T GetProperty<T>(this HttpRequestMessage request, string key)
        {
            T value = default(T);
            object @object = null;
            request.Properties.TryGetValue(key, out @object);
            if (@object is T)
            {
                value = (T)@object;
            }
            else
            {
                throw new InvalidCastException(string.Format("无效类型转换：{0}", typeof(T).FullName));
            }
            return value;
        }
        
    }