How do I monitor the progress of a file transfer in Apache Commons VFS?

Using Apache Commons VFS, how do I monitor the progress of a file transfer. I need to be able to do it with uploads and downloads. I also need to monitor progress over HTTP, FTP, SFTP and FTPS. I can't find anything in the documentation about it.

It can be done by getting input and output streams from VFS. The following example uses a utility class from commons-net (a dependency of VFS) to manage the copying and progress-monitoring. You could equally do it manually.

import org.apache.commons.net.io.Util;
import org.apache.commons.net.io.CopyStreamListener;

private void copy(FileObject sourceFile, FileObject destinationFile, CopyStreamListener progressMonitor) throws IOException {
    InputStream sourceFileIn = sourceFile.getContent().getInputStream();
    try {
        OutputStream destinationFileOut = destinationFile.getContent().getOutputStream();
        try {
            Util.copyStream(sourceFileIn, destinationFileOut, Util.DEFAULT_COPY_BUFFER_SIZE, sourceFile.getContent().getSize(), progressMonitor);
        } finally {
            destinationFileOut.close();
        }
    } finally {
        sourceFileIn.close();
    }
}