//把流转化为文件

 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();

        }

//把流转化为字节数组

        public static byte[] StreamToBytes(Stream stream)

        {

            MemoryStream memoryStream = new MemoryStream();

            stream.CopyTo(memoryStream);

            return memoryStream.ToArray();

        }

//把流转化为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字符串转化为流

      　pubblic static Stream StringToStream(string str)

　　　　{

　　　　　　　byte[] bt = Convert.FromBase64String(str);

            System.IO.MemoryStream stream = new System.IO.MemoryStream(bt);

　　　　}

求补充。。。。。。。。。。。。。。