if (event.getBlockPlaced().getType().equals(Material.LECTERN) && event.getBlockPlaced().getState() instanceof Lectern &&
    (event.getItemInHand().getType().equals(Material.WRITTEN_BOOK) || event.getItemInHand().getType().equals(Material.WRITABLE_BOOK))) {
  Lectern lectern = (Lectern) event.getBlockPlaced().getState();
  // Do whatever with Lectern object here.
}