将Stream写入文件

        /// <summary> 
        /// 将 Stream 写入文件 
        /// </summary> 
        public static FileStream StreamToFile(Stream stream, string fileName)
        {
            // 把 Stream 转换成 byte[] 
            byte[] bytes = new byte[stream.Length];
            stream.Read(bytes, 0, bytes.Length);
            // 设置当前流的位置为流的开始 
            stream.Seek(0, SeekOrigin.Begin);

            // 把 byte[] 写入文件 
            FileStream fs = new FileStream(fileName, FileMode.Create);
            BinaryWriter bw = new BinaryWriter(fs);
            bw.Write(bytes);
            bw.Close();
            fs.Close();

            return fs;
        }