Simple tool to ping a Minecraft server to get MOTD, online players and max players.

ServerPinger.java

/*
 * MIT License.
 *
 * Copyright (c) 2021 MrMicky
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package fr.mrmicky.testproject.tools;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionException;

/**
 * Simple tool to ping a Minecraft server to get MOTD, online players and max players.
 *
 * @author MrMicky
 */
public class ServerPinger {

    public static CompletableFuture<PingResult> ping(String address) {
        return ping(address, 25565);
    }

    public static CompletableFuture<PingResult> ping(String address, int port) {
        return ping(new InetSocketAddress(address, port), 1000);
    }

    public static CompletableFuture<PingResult> ping(InetSocketAddress address, int timeout) {
        return CompletableFuture.supplyAsync(() -> {
            try (Socket socket = new Socket()) {

                socket.setSoTimeout(timeout);
                socket.connect(address, timeout);

                try (DataOutputStream out = new DataOutputStream(socket.getOutputStream());
                     InputStream in = socket.getInputStream();
                     InputStreamReader reader = new InputStreamReader(in, StandardCharsets.UTF_16BE)) {

                    out.write(new byte[]{(byte) 0xFE, 0x01});

                    int packetId = in.read();
                    int length = reader.read();

                    if (packetId != 0xFF) {
                        throw new IOException("Invalid packet id: " + packetId);
                    }

                    if (length <= 0) {
                        throw new IOException("Invalid length: " + length);
                    }

                    char[] chars = new char[length];

                    if (reader.read(chars, 0, length) != length) {
                        throw new IOException("Premature end of stream");
                    }

                    String string = new String(chars);

                    if (!string.startsWith("§")) {
                        throw new IOException("Unexpected response: " + string);
                    }

                    String[] data = string.split("\000");

                    int players = Integer.parseInt(data[4]);
                    int maxPlayers = Integer.parseInt(data[5]);

                    return new PingResult(players, maxPlayers, data[3]);
                }
            } catch (IOException e) {
                throw new CompletionException(e);
            }
        });
    }

    public static class PingResult {

        private final int players;
        private final int maxPlayers;
        private final String motd;

        public PingResult(int players, int maxPlayers, String motd) {
            this.players = players;
            this.maxPlayers = maxPlayers;
            this.motd = motd;
        }

        public int getPlayers() {
            return this.players;
        }

        public int getMaxPlayers() {
            return this.maxPlayers;
        }

        public String getMotd() {
            return this.motd;
        }

        @Override
        public String toString() {
            return "PingResult{players=" + this.players + ", maxPlayers=" + this.maxPlayers + '}';
        }
    }
}

ServerPinger.md

Server Pinger

Simple tool to ping a Minecraft server to get MOTD, online players and max players.

Usage

Use ServerPinger#ping, which returns a CompletableFuture<PingResult> (see CompletableFuture's JavaDoc).

Example

Non-blocking

ServerPinger.ping("funcraft.net") // The port can be specified as the second argument (25565 by default)
        .thenAccept(result -> {
            System.out.println("=== Ping result ===");
            System.out.println("Online players: " + result.getPlayers());
            System.out.println("Max players: " + result.getMaxPlayers());
            System.out.println("MOTD: " + result.getMotd());
        })
        .exceptionally(ex -> {
            ex.printStackTrace();

            return null;
        });

Blocking

try {
    ServerPinger.PingResult result = ServerPinger.ping("funcraft.net").get();

    System.out.println("=== Ping result ===");
    System.out.println("Online players: " + result.getPlayers());
    System.out.println("Max players: " + result.getMaxPlayers());
    System.out.println("MOTD: " + result.getMotd());
} catch (Exception ex) {
    ex.printStackTrace();
}

License

MIT

how?

how

@Yumileashen @HiroDeveloper Hi, I've updated this Gist with examples :)