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public string PostFormData(List<FormItem> list, string uri)
        {
            string boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");

            //请求
            WebRequest req = WebRequest.Create(uri);
            req.Method = "POST";
            req.ContentType = "multipart/form-data; boundary=" + boundary;

            //组织表单数据
            StringBuilder sb = new StringBuilder();
            foreach (FormItem item in list)
            {
                switch (item.ParamType)
                {
                    case ParamType.Text:
                        sb.Append("--" + boundary);
                        sb.Append("\r\n");
                        sb.Append("Content-Disposition: form-data; name=\"" + item.Name + "\"");
                        sb.Append("\r\n\r\n");
                        sb.Append(item.Value);
                        sb.Append("\r\n");
                        break;
                    case ParamType.File:
                        sb.Append("--" + boundary);
                        sb.Append("\r\n");
                        sb.Append("Content-Disposition: form-data; name=\"" + item.Name + "\"; filename=\"" + item.Value + "\"");
                        sb.Append("\r\n");
                        sb.Append("Content-Type: application/octet-stream");
                        sb.Append("\r\n\r\n");
                        break;
                }
            }

            string head = sb.ToString();
            //post字节总长度
            long length = 0;
            byte[] form_data = Encoding.UTF8.GetBytes(head);

            //结尾
            byte[] foot_data = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");
            List<FormItem> fileList = list.Where(f => f.ParamType == ParamType.File).ToList();
            length = form_data.Length + foot_data.Length;
            foreach (FormItem fi in fileList)
            {
                FileStream fileStream = new FileStream(fi.Value, FileMode.Open, FileAccess.Read);
                length += fileStream.Length;
                fileStream.Close();
            }

            req.ContentLength = length;
            Stream requestStream = req.GetRequestStream();

            //发送表单参数
            requestStream.Write(form_data, 0, form_data.Length);
            foreach (FormItem fd in fileList)
            {
                FileStream fileStream = new FileStream(fd.Value, FileMode.Open, FileAccess.Read);
                //文件内容
                byte[] buffer = new Byte[checked((uint)Math.Min(4096, (int)fileStream.Length))];
                int bytesRead = 0;
                while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
                    requestStream.Write(buffer, 0, bytesRead);

                //结尾
                requestStream.Write(foot_data, 0, foot_data.Length);
            }
            requestStream.Close();

            //响应
            WebResponse pos = req.GetResponse();
            StreamReader sr = new StreamReader(pos.GetResponseStream(), Encoding.UTF8);
            string html = sr.ReadToEnd().Trim();
            sr.Close();

            if (pos != null)
            {
                pos.Close();
                pos = null;
            }
            if (req != null)
            {
                req = null;
            }
            return html;
        }

        public string SaveFileFromUrl(string fileName, string url)
        {
            WebResponse response = null;
            Stream stream = null;
            try
            {
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
                response = request.GetResponse();
                stream = response.GetResponseStream();
                if (!response.ContentType.ToLower().StartsWith("text/"))
                {
                    SaveBinaryFile(response, fileName);
                }
                else
                {
                    StreamReader sr = new StreamReader(stream, System.Text.Encoding.UTF8);
                    return sr.ReadToEnd();
                }
            }
            catch (Exception err)
            {
                return err.ToString();
            }
            return "complete";
        }

        public bool SaveBinaryFile(WebResponse response, string fileName)
        {
            bool value = true;
            byte[] buffer = new byte[1024];
            try
            {
                if (System.IO.File.Exists(fileName))
                    System.IO.File.Delete(fileName);
                Stream outStream = System.IO.File.Create(fileName);
                Stream inStream = response.GetResponseStream();
                int l;
                do
                {
                    l = inStream.Read(buffer, 0, buffer.Length);
                    if (l > 0)
                        outStream.Write(buffer, 0, l);
                }
                while (l > 0);
                outStream.Close();
                inStream.Close();
            }
            catch
            {
                value = false;
            }
            return value;
        }

        public class FormItem
        {
            public string Name { get; set; }
            public ParamType ParamType { get; set; }
            public string Value { get; set; }
        }

        public enum ParamType
        {
            Text,
            File
        }