应用程序中向web服务post多文件和post参数

 public static string UploadFileEx( string url,
            System.Web.HttpFileCollection files, NameValueCollection querystring
            )
        {
            string boundary = "----------" + DateTime.Now.Ticks.ToString("x");
            HttpWebRequest webrequest = (HttpWebRequest)WebRequest.Create(new Uri(url));
            webrequest.ContentType = "multipart/form-data; boundary=" + boundary;
            webrequest.Method = "POST";
            List<FileInfo_Stream> fileStream = null;
            if (files.Count > 0)
            {
                fileStream = new List<FileInfo_Stream>();
                foreach (var file in files.Keys)
                {
                    StringBuilder sb = new StringBuilder();
                    sb.Append("--");
                    sb.Append(boundary);
                    sb.Append("\r\n");
                    sb.Append("Content-Disposition: form-data; name=\"");
                    sb.Append(file.ToString());
                    sb.Append("\"; filename=\"");
                    sb.Append(files[file.ToString()].FileName);
                    sb.Append("\"");
                    sb.Append("\r\n");
                    sb.Append("Content-Type: ");
                    sb.Append(files[file.ToString()].ContentType);
                    sb.Append("\r\n");
                    sb.Append("\r\n");
                    FileInfo_Stream fs=new FileInfo_Stream();
                    fs.postHeaderBytes=Encoding.UTF8.GetBytes(sb.ToString());
                    fs.stream=files[file.ToString()].InputStream;
                    fileStream.Add(fs);
                }
            }
            StringBuilder sb1 = new StringBuilder();
            foreach (var key in querystring.Keys)
            {
                sb1.Append("--");
                sb1.Append(boundary);
                sb1.Append("\r\n");
                sb1.Append("Content-Disposition: form-data; name=\""+key.ToString()+"\"");
                sb1.Append("\r\n");
                sb1.Append("\r\n");
                sb1.Append(querystring[key.ToString()].ToString());
                sb1.Append("\r\n");
            }
            //byte[] postHeaderBytes = Encoding.UTF8.GetBytes(sb.ToString());
            byte[] boundaryBytes = Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");
            byte[] postDate = Encoding.UTF8.GetBytes(sb1.ToString());
            long length = fileStream.Sum(s1=>s1.postHeaderBytes.Length) +fileStream.Sum(s2=>s2.stream.Length)+ (boundaryBytes.Length * fileStream.Count) + postDate.Length;
            webrequest.ContentLength = length;
            Stream requestStream = webrequest.GetRequestStream();
            requestStream.Write(postDate, 0, postDate.Length);
            foreach (var fs in fileStream)
            {
                requestStream.Write(fs.postHeaderBytes, 0, fs.postHeaderBytes.Length);
                byte[] buffer = new Byte[checked((uint)Math.Min(4096, (int)fs.stream.Length))];
                int bytesRead = 0;
                while ((bytesRead = fs.stream.Read(buffer, 0, buffer.Length)) != 0)
                    requestStream.Write(buffer, 0, bytesRead);
                requestStream.Write(boundaryBytes, 0, boundaryBytes.Length);
            }
            webrequest.Timeout = 1000000;
            WebResponse responce = webrequest.GetResponse();
            Stream s = responce.GetResponseStream();
            StreamReader sr = new StreamReader(s);
            string str = sr.ReadToEnd();
            foreach (var filestream1 in fileStream)
            {
                filestream1.stream.Close();
            }
            requestStream.Close();
            sr.Close();
            s.Close();
            responce.Close();
            return str;
        }
        
    }
    public class FileInfo_Stream
    {
        public Stream stream { get; set; }
        public byte[] postHeaderBytes { get; set; }
    }