Possible Listener

public class PlayerJoinListener {

    public void execute (PlayerJoinEvent e) {
        Player player = e.getPlayer();
        LoginCheck lc = new LoginCheck();

        // Construct the IP Address String
        InetSocketAddress a = player.getAddress();
        InetAddress iNetAddress = a.getAddress();
        String address = iNetAddress.getHostAddress();
        StringBuilder ip = new StringBuilder();
        for (int i = 0; i < address.length(); i++) {
            if ((address.charAt(i) >= '0' && address.charAt(i) <= '9') || address.charAt(i) == '.') {
                ip.append(address.charAt(i));
            } else if (address.charAt(i) == ':') {
                break;
            }
        }

        IPcheck.ipToCheck = ip.toString();
        IPcheck.backend.log(player.getName(), ip.toString());
        IPcheck.shouldCheck = true;

        if (Configuration.secureMode) {
            IPcheck.shouldCheck = lc.secureCheck(ip.toString(), e);
        }

        LoginReport lp = new LoginReport();

        // Do not perform check on operators or players with the "ipcheck.getnotify permission.
        if (!player.isOp() && !player.hasPermission("ipcheck.getnotify")) {
            if (Configuration.notifyLogin && IPcheck.shouldCheck) {
                int accounts = (IPcheck.backend.getAlts(IPcheck.ipToCheck)).size();
                Player playerCheck = e.getPlayer();
                lp.execute(IPcheck.ipToCheck, playerCheck, accounts);
            }
        }

        return;
    }

}

public class LoginCheck {

    public boolean secureCheck(String ip, PlayerJoinEvent e) {
        ArrayList<String> players = IPcheck.backend.getAlts(ip);
        int accounts = players.size();
        Player player = e.getPlayer();
        return secureKick(accounts, player.getName(), e, ip);
    }

    public boolean secureKick(int accounts, String player, PlayerJoinEvent e, String ip) {
        // If the player was reported to have more than the secure-threshold # of accounts, then kick (if not exempt).
        if (accounts > Configuration.secureThreshold && !Configuration.isExemptPlayer(player) && !Configuration.isExemptIp(ip)) {

            if (player != null) {
                Player kickPlayer = e.getPlayer();
                kickPlayer.kickPlayer(Configuration.secureKickMsg);
                return false;
            }
        }

        return true;
    }

}