code: private static void addDataEventListenerToPeer(Executor executor, Peer peer, PeerDataEventListener downloadListener) {
          peer.addBlocksDownloadedEventListener(executor, downloadListener);
          peer.addChainDownloadStartedEventListener(executor, downloadListener);
          peer.addGetDataEventListener(executor, downloadListener);
          peer.addPreMessageReceivedEventListener(executor, downloadListener);
      }
docs: Register a data event listener against a single peer (i.e. for blockchain
  download). Handling registration/deregistration on peer death/add is
  outside the scope of these methods.