string url = url + "webUploadFile";

            Uri server = new Uri(url);

            HttpClient httpClient = new HttpClient();

            MultipartFormDataContent multipartFormDataContent = new MultipartFormDataContent();

            StreamContent streamConent = new StreamContent(new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read));

            multipartFormDataContent.Add(streamConent, "jpg", fileName);

            HttpResponseMessage responseMessage = httpClient.PostAsync(server, multipartFormDataContent).Result;

            return responseMessage;

[Route("webUploadFile"), System.Web.Http.HttpPost]
public HttpResponseMessage webUploadFile()

{

　　if (HttpContext.Current.Request.Files.AllKeys.Any())

                {var httpPostedFiles = HttpContext.Current.Request.Files;

                    if (httpPostedFiles != null && httpPostedFiles.Count > )

                    {

                        // 获取文件

                        HttpPostedFile httpPostedFile = httpPostedFiles[];

                        string fileExtension = ".jpg";// Path.GetExtension(httpPostedFile.FileName);// 文件扩展名

                        string fileId = "";

                        string filePath = uploadPath + fileId + fileExtension;// 上传路径

                        httpPostedFile.SaveAs(filePath);

                        string jsonres = "{\"code\":\"200\",\"message\":\"文件上传成功\", \"data\":{ \"fileUrl\":\"" + downloadurl+ "webDownloadFile?fileId=" + fileId + "\"}}";

                        return new HttpResponseMessage(HttpStatusCode.OK) { Content = new StringContent(jsonres, System.Text.Encoding.UTF8, "application/json")};

                    }

                }
}

[Route("webDownloadFile"), System.Web.Http.HttpGet]

        public HttpResponseMessage webDownloadFile()

        {

            if (HttpContext.Current.Request.Params.Count >  && HttpContext.Current.Request["fileId"] != null)

            {

                string fileId = HttpContext.Current.Request["fileId"];

                string fileName = fileId + ".jpg";

                string path = uploadPath + fileName;

                if (!File.Exists(path))

                {

                    return new HttpResponseMessage(HttpStatusCode.NotFound) { Content = new StringContent(Common.ReturnMessage("", "文件不存在"), System.Text.Encoding.UTF8, "application/json") };

                }

                HttpResponseMessage result = null;

                FileStream fs = new FileStream(path, FileMode.Open);

                result = new HttpResponseMessage(HttpStatusCode.OK);

                result.Content = new StreamContent(fs);

                result.Content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("image/jpeg");

                return result;

            }

            return new HttpResponseMessage(HttpStatusCode.BadRequest) { Content = new StringContent(Common.ReturnMessage("", "文件下载失败"), System.Text.Encoding.UTF8, "application/json") };

        }