将byte[]类型的数据，转化为文件存在硬盘中

                byte[] filebyte = mimeEntity.Data; 
                FileStream fs = new FileStream(MapPath("Attachments/" + fileName), FileMode.CreateNew);
                BinaryWriter bw = new BinaryWriter(fs);
                bw.Write(filebyte, 0, filebyte.Length);
                bw.Close();
                fs.Close();