code: @Override
      public void transferProgressed(TransferEvent event) {
          TransferResource resource = event.getResource();
  
          long lastTransferred = downloads.get(resource);
          long transferred = event.getTransferredBytes();
  
          if (transferred - lastTransferred >= TRANSFER_THRESHOLD) {
              downloads.put(resource, Long.valueOf(transferred));
              long total = resource.getContentLength();
              log.finer(getStatus(transferred, total) + ", ");
          }
      }
docs: /*
  (non-Javadoc)
  
  @see org.sonatype.aether.util.listener.AbstractTransferListener#transferProgressed
  (org.sonatype.aether.transfer.TransferEvent)