public void StreamToFile(Stream stream,string fileName)
{
// 把 Stream 轉換成 byte[]
byte[] bytes = new byte[stream.Length];
stream.Read(bytes, 0, bytes.Length);
// 設置當前流的位置為流的開始
stream.Seek(0, SeekOrigin.Begin);
// 把 byte[] 寫入文件
FileStream fs = new FileStream(fileName, FileMode.Create);
BinaryWriter bw = new BinaryWriter(fs);
bw.Write(bytes);
bw.Close();
fs.Close();
}