How to show downloading progress by FTPClient(Apache commons-net component)

When we use apache commons-net FTPClient component to download file from FTP server, How to show the progress?

we can use this method: 

ftpClient.retrieveFile(source, outputStream);

But this method does't show the progress, so we should use another way as below:

OutputStream os = null;
CountingOutputStream cos = null;
try {
	os = Files.newOutputStream(Paths.get(destination));
	cos = new CountingOutputStream(os) {
		protected void beforeWrite(int n){
			super.beforeWrite(n);
			int downloadedSize = getCount();
			double d = (double) downloadedSize / fileSize;
			int currentPercent = (int) (d * 100);
			if (currentPercent > previousPercent.get()) {
				previousPercent.set(currentPercent);
				log.info("\nDownloaded {}:" + getCount() + "/" + fileSize + " percent: {}%", source, currentPercent);
			}
		}
	};
	ftpClient.enterLocalPassiveMode();
    ftpClient.retrieveFile(source, cos);

}catch (IOException e) {
	log.error("download file {} error", source, e);
	throw new RuntimeException(e);
} finally {	
	IOUtils.closeQuietly(os, cos);
}

From：Is Everything OK