#region 异步返回文件流(提高应用程序的吞吐能力)

        public async Task<ActionResult> AwaitFile()

        {

            var responseHtml = await GetResponseStream("http://static.xuexiba.com/uploadfile/UserInfo/Avatar/201311/1302844759237319155175.jpg");

            return File(responseHtml, "image/jpeg");

        }

        private async Task<Stream> GetResponseStream(string url)

        {

            return await GetResponseContentAsync(url);

        }

        private async Task<Stream> GetResponseContentAsync(string url)

        {

            var httpClient = new System.Net.Http.HttpClient();

            var response = await httpClient.GetAsync(url);

            if (response.StatusCode == System.Net.HttpStatusCode.OK)

            {

                return await response.Content.ReadAsStreamAsync();

            }

            else

            {

                return null;//error

            }

        }

        #endregion

#region 异步返回文本(提高应用程序的吞吐能力)

        public async Task<ActionResult> AwaitHtml()

        {

            var responseHtml = await GetResponseHtml("http://www.sina.com");

            return Content(responseHtml);

        }

        private async Task<string> GetResponseHtml(string url)

        {

            return await GetResponseStringAsync(url);

        }

        private async Task<string> GetResponseStringAsync(string url)

        {

            var httpClient = new System.Net.Http.HttpClient();

            var response = await httpClient.GetAsync(url);

            if (response.StatusCode == System.Net.HttpStatusCode.OK)

            {

                return await response.Content.ReadAsStringAsync();//加await的意思是说，主ＵＩ等待它执行完成后，再继续执行，这种就叫作并行！

            }

            else

            {

                return null;//error

            }

        }

        #endregion