Echo client/server pair

scratch_2.java

import org.apache.commons.codec.digest.DigestUtils;
import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.RandomUtils;
import org.apache.commons.lang3.StringUtils;

import java.io.IOException;
import java.net.*;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.List;
import java.util.Locale;
import java.util.Scanner;
import java.util.stream.Stream;

class EchoClient {
    private byte[] buffer = new byte[128];
    private DatagramSocket socket;
    private InetAddress address;
    private Scanner commandLine = new Scanner(System.in);
    private boolean isRunning = true;

    public EchoClient() throws IOException {
        socket = new DatagramSocket();
        address = InetAddress.getByName("localhost");

        Scanner scan = new Scanner(System.in);
        System.out.print(">> ");
        String line = scan.nextLine();
        while(isRunning) {
            if(line.startsWith("end")) {
                System.out.println("closing...");
                isRunning = false;
                socket.close();
                System.exit(0);
            } else {
                if(!line.isEmpty()) {
                    String[] a =  StringUtils.split(line);
                    List<String> b = Arrays.stream(a).map(v -> v.trim().toLowerCase()).toList();
                    a = b.toArray(new String[b.size()]);

                    if(a.length == 1) {
                        // no arguments taken, just run the job
                    } else if(a.length > 1) {
                        String command = a[0];
                        String[] args = ArrayUtils.subarray(a, 1, a.length);

                        procCommand(command, args);
                    } else {

                    }
                }
            }

            System.out.print(">> ");
            line = scan.nextLine();
        }
    }

    private void procCommand(String command, String[] args) throws IOException {
        switch(command) {
            case "send":
                if(args.length > 0) sendEcho(StringUtils.join(args, " "));
                break;
        }
    }

    public String sendEcho(String msg) throws IOException {
        buffer = msg.getBytes(StandardCharsets.UTF_8);
        DatagramPacket packet = new DatagramPacket(buffer, buffer.length, address, 6881);
        socket.send(packet);
        packet = new DatagramPacket(buffer, buffer.length);
        socket.receive(packet);
        String received = new String(packet.getData(), 0, packet.getLength());
        System.out.println("from client: " + received);

        return received;
    }

    public void close() {
        socket.close();
    }
}

class EchoServer extends Thread {
    private DatagramSocket socket;
    private boolean isRunning = false;
    private byte[] buffer = new byte[128];

    public EchoServer() throws SocketException {
        socket = new DatagramSocket(6881);
    }

    @Override
    public void run() {
        isRunning = true;

        while(isRunning) {

            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            try {
                socket.receive(packet);
            } catch (IOException e) {
                e.printStackTrace();
            }

            InetAddress address = packet.getAddress();
            int port = packet.getPort();
            packet = new DatagramPacket(buffer, buffer.length, address, port);
            String received = new String(packet.getData(), 0, packet.getLength());
            System.out.println("from server: " + received);

            if(received.equals("end")) {
                isRunning = false;
                continue;
            }

            try {
                socket.send(packet);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        socket.close();
    }
}

class Scratch {
    private static EchoClient client;

    public static void main(String[] args) throws IOException {
        new EchoServer().start();
        client = new EchoClient();


        /*

        String echo = client.sendEcho("hello, dork!");
        echo = client.sendEcho("server is working.");
        client.sendEcho("end");
        client.close();
        */
    }
}