Stream 和 文件之间的转换

/// <summary>
        /// 将 Stream 写入文件
        /// </summary>
        public void 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();
        }
        /// <summary>
        /// 从文件读取 Stream
        /// </summary>
        public Stream FileToStream(string fileName)
        {
            // 打开文件
            FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read);
            // 读取文件的 byte[]
            byte[] bytes = new byte[fileStream.Length];
            fileStream.Read(bytes, 0, bytes.Length);
            fileStream.Close();
            // 把 byte[] 转换成 Stream
            Stream stream = new MemoryStream(bytes);
            return stream;
        }