//把流轉化為文件
 public static void StreamToFile(Stream stream, string filepath)
        {
            byte[] bytes = StreamToBytes(stream);
            FileStream fileStream = new FileStream(filepath, FileMode.Create);
            fileStream.Write(bytes, 0, bytes.Length);
            fileStream.Flush();
            fileStream.Close();
        }
//把流轉化為字節數組
        public static byte[] StreamToBytes(Stream stream)
        {
            MemoryStream memoryStream = new MemoryStream();
            stream.CopyTo(memoryStream);
            return memoryStream.ToArray();
        }
//把流轉化為Base64字符串

        public static string StreamToString(Stream stream)
        {

            byte[] buffer = new byte[stream.Length];
            stream.Read(buffer, 0, (int)stream.Length);
            string base64string = Convert.ToBase64String(buffer);
            return base64string;
        }

//把Base64字符串轉化為流

      　pubblic static Stream StringToStream(string str)
　　　　{
　　　　　　　byte[] bt = Convert.FromBase64String(str);
            System.IO.MemoryStream stream = new System.IO.MemoryStream(bt);
　　　　}

求補充。。。。。。。。。。。。。。