code: public List<Message> requestFolderMenuFrom(final SlotReference slotReference, final int sortOrder, final int folderId)
              throws Exception {
  
          ConnectionManager.ClientTask<List<Message>> task = new ConnectionManager.ClientTask<List<Message>>() {
              @Override
              public List<Message> useClient(Client client) throws Exception {
                  if (client.tryLockingForMenuOperations(MetadataFinder.MENU_TIMEOUT, TimeUnit.SECONDS)) {
                      try {
                          logger.debug("Requesting Key menu.");
                          Message response = client.menuRequestTyped(Message.KnownType.FOLDER_MENU_REQ, Message.MenuIdentifier.MAIN_MENU, slotReference.slot,
                                  CdjStatus.TrackType.UNANALYZED, new NumberField(sortOrder), new NumberField(folderId), new NumberField(0xffffff));
                          return client.renderMenuItems(Message.MenuIdentifier.MAIN_MENU, slotReference.slot, CdjStatus.TrackType.UNANALYZED, response);
                      } finally {
                          client.unlockForMenuOperations();
                      }
                  } else {
                      throw new TimeoutException("Unable to lock player for menu operations.");
                  }
              }
          };
  
          return ConnectionManager.getInstance().invokeWithClientSession(slotReference.player, task, "requesting folder menu");
      }
docs: Ask the specified player for a Folder menu for exploring its raw filesystem.
  This is a request for unanalyzed items, so we do a typed menu request.
  
  @param slotReference the player and slot for which the menu is desired
  @param sortOrder the order in which responses should be sorted, 0 for default, see Section 6.11.1 of the
  <a href="https://github.com/Deep-Symmetry/dysentery/blob/master/doc/Analysis.pdf">Packet Analysis
  document</a> for details
  @param folderId identifies the folder whose contents should be listed, use -1 to get the root folder
  
  @return the entries in the folder menu
  
  @throws Exception if there is a problem obtaining the menu