public class Server {

    public static void main(String[] args) {

        ExecutorService executorService = Executors.newFixedThreadPool(10);

        try(DatagramSocket serverSocket = new DatagramSocket(8888)) {

            while(true) {

                byte[] receiveData =                        new byte[64];
                DatagramPacket receivePacket =              new DatagramPacket(receiveData, receiveData.length);
                serverSocket.receive(receivePacket);

                executorService.submit(new ConnectThread(receivePacket));

            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            executorService.shutdown();
        }

    }

    static class ConnectThread
        implements Runnable {

        private DatagramPacket receivePacket;

        ConnectThread(DatagramPacket receivePacket) {
            this.receivePacket = receivePacket;
        }

        @Override
        public void run() {
            System.out.println(new String(receivePacket.getData()));
        }
    }

}

public class Client {

    public static void main(String[] args) {

        send("send1");
        send("send2");
        send("send3");
        send("send4");
        send("send5");
        send("send6");

    }

    private static void send(String str) {

        try(DatagramSocket clientSocket = new DatagramSocket()) {
            clientSocket.send(new DatagramPacket(str.getBytes(), str.getBytes().length,
                 InetAddress.getByName("127.0.0.1"), 8888));
        }
        catch (IOException e) {
            e.printStackTrace();
        }
    }

}