public class JoinListener implements Listener {

    @EventHandler
    public void onPreLogin(PlayerLoginEvent event) {
        String banReason = MySQL.getBannedReason(event.getPlayer().getUniqueId());
        if (banReason != null) {
            event.setResult(PlayerLoginEvent.Result.KICK_OTHER);
            event.setKickMessage(banReason);
        }
    }
}