--------------- CLASE ServerPinger ---------------
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.charset.Charset;

import com.google.gson.JsonObject;
import com.google.gson.JsonParser;

public class ServerPinger {

    public static ConnectionData ping(String ip, int port) {
        try {
            InetSocketAddress address = new InetSocketAddress(ip, port);

            Socket socket = new Socket();

            socket.setSoTimeout(1200);

            socket.connect(address, 1200);

            ByteArrayOutputStream bs = new ByteArrayOutputStream();

            DataOutputStream out = new DataOutputStream(bs);

            out.write(0x00); // ID de paquete

            int version = 4; // ID de versión

            writeInt(version, out);

            writeString(address.getHostString(), out);

            out.writeShort(address.getPort());

            writeInt(1, out);

            DataOutputStream out2 = new DataOutputStream(socket.getOutputStream());

            sendPacket(bs.toByteArray(), out2);

            out.close();

            bs.close();

            sendPacket(new byte[]{ 0x00 }, out2);

            DataInputStream in = new DataInputStream(socket.getInputStream());

            readInt(in); // Esto es algo que realmente ni utilizamos, pero hay que leerlo, porque si no falla

            int packetId = readInt(in);

            if (packetId != 0x00) {
                socket.close();

                throw new RuntimeException("PacketId incorrecto.");
            }

            int strLength = readInt(in);

            if (strLength < 1) {
                socket.close();

                throw new RuntimeException("Tamaño de string demasiado corto.");
            }

            byte[] responseData = new byte[strLength];

            in.readFully(responseData);

            in.close();

            out2.close();

            socket.close();

            String json = new String(responseData, Charset.forName("utf-8"));

            JsonObject object = new JsonParser().parse(json).getAsJsonObject();

            String motd = object.get("description").getAsString();

            int players = object.get("players").getAsJsonObject().get("online").getAsInt();

            int max = object.get("players").getAsJsonObject().get("max").getAsInt();

            return new ConnectionData(Status.ONLINE, motd, players, max);
        } catch (IOException ex) {
            return new ConnectionData(Status.OFFLINE);
        }
    }

    static void writeInt(int i, DataOutputStream out) throws IOException {
        while (true) {
            if ((i & 0xFFFFFF80) == 0) {
                out.write(i);

                return;
            }

            out.write(i & 0x7F | 0x80);

            i >>>= 7;
        }
    }

    static void writeString(String str, DataOutputStream out) throws IOException {
        writeInt(str.length(), out);

        out.write(str.getBytes(Charset.forName("utf-8")));
    }

    static void sendPacket(byte[] data, DataOutputStream out) throws IOException {
        writeInt(data.length, out);

        out.write(data);
    }

    static int readInt(DataInputStream in) throws IOException {
        int i = 0;

        int j = 0;

        while (true) {
            int k = in.readByte();

            i |= (k & 0x7F) << j++ * 7;

            if (j > 5) {
                throw new RuntimeException("Int demasiado grande.");
            }

            if ((k & 0x80) != 128) {
                break;
            }
        }

        return i;
    }

    public static class ConnectionData {
        Status status;

        String motd;

        int players, max;

        public ConnectionData(Status status) {
            this.status = status;
        }

        public ConnectionData(Status status, String motd, int players, int max) {
            this.status = status;
            this.motd = motd;
            this.players = players;
            this.max = max;
        }

        public Status getStatus() {
            return status;
        }

        public String getMotd() {
            return motd;
        }

        public int getPlayers() {
            return players;
        }

        public int getMaxPlayers() {
            return max;
        }
    }

    public enum Status {
        ONLINE, OFFLINE;
    }
}

--------------- Ejemplo ---------------

public class Prueba {

    public static void main(String[] args) {
        ConnectionData data = ServerPinger.ping("192.99.4.13", 11701);

        System.out.println(data.getMotd());
        System.out.println(data.getPlayers());
        System.out.println(data.getMaxPlayers());
    }
}