压缩文件

示例代码：

       string filepath = Server.MapPath("Textfile.txt");        FileStream infile = File.OpenRead(filepath);        byte[] buffer = new byte[infile.Length];        infile.Read(buffer, 0, buffer.Length);        infile.Close();        FileStream outfile=File.Create(Path.ChangeExtension(filepath,"zip"));        GZipStream gzipstream=new GZipStream(outfile,CompressionMode.Compress);        gzipstream.Write(buffer,0,buffer.Length);        gzipstream.Close();