Socket Programming using Threading

public class Server {
    private static int clientCount = 0;
    private static final int MAX_CLIENTS = 5;

    public static void main(String[] args) throws IOException {
        ServerSocket handshake =  new ServerSocket(4000);
        System.out.println("Server started at: " + handshake.getLocalPort());
        System.out.println("Waiting for Clients...");

        while (clientCount < MAX_CLIENTS) {
            Socket socket = handshake.accept();
            clientCount++;
            System.out.println("A new client is connected" + socket);
            DataOutputStream output_stream = new DataOutputStream(socket.getOutputStream());
            DataInputStream input_stream = new DataInputStream(socket.getInputStream());
            System.out.println("A new thread is assigning");
            Thread new_tunnel = new ClientHandler(socket, input_stream, output_stream);
            new_tunnel.start();
        }

        System.out.println("Sever has reached it's maximum capacity. Shutting down!");
        handshake.close();
    }
}

public class ClientHandler extends Thread {
    final Socket com_tunnel;
    final DataInputStream dis_tunnel;
    final DataOutputStream dos_tunnel;

    public ClientHandler(Socket s, DataInputStream dis, DataOutputStream dos)
    {
        this.com_tunnel = s;
        this.dis_tunnel = dis;
        this.dos_tunnel = dos;
    }

    public void run() {
        while(true){
            try {
                dos_tunnel.writeUTF("Send a number or type 'Exit' to disconnect:");
                String received = dis_tunnel.readUTF();

                if(received.equalsIgnoreCase("Exit")){
                    System.out.println("Client " + this.com_tunnel + " sends exit");
                    System.out.println("Closing the connection");
                    this.com_tunnel.close();
                    break;
                }

                try {
                    int number = Integer.parseInt(received);
                    List<Integer> primes = findPrimes(number);
                    dos_tunnel.writeUTF("The prime numbers are: " + primes);
                } catch (NumberFormatException e) {
                    dos_tunnel.writeUTF("Invalid input. Please send a valid number.");
                }

            } catch (IOException ex) {
                System.err.println("Error: " + ex.getMessage());
                break;
            }
        }
        try {
            this.dos_tunnel.close();
            this.dis_tunnel.close();
        } catch (IOException ex) {
            System.err.println("Error closing resources: " + ex.getMessage());
        }
    }

    private List<Integer> findPrimes(int num) {
        List<Integer> primes = new ArrayList<>();
        for (int i = 2; i <= num; i++) {
            if (isPrime(i)) {
                primes.add(i);
            }
        }
        return primes;
    }

    private boolean isPrime(int n) {
        if (n <= 1) return false;
        for (int i = 2; i <= Math.sqrt(n); i++) {
            if (n % i == 0) return false;
        }
        return true;
    }
}

public class Client {
    public static void main(String[] args)throws IOException {
        try {
            Socket clientSocket = new Socket("localhost", 4000);
            System.out.println("Connected at server Handshaking port " + clientSocket.getPort());
            System.out.println("Client is connecting at Communication Port " + clientSocket.getLocalPort());
            System.out.println("Client is Connected");

            Scanner scn = new Scanner(System.in);
            DataOutputStream dos = new DataOutputStream(clientSocket.getOutputStream());
            DataInputStream dis = new DataInputStream(clientSocket.getInputStream());

            while(true){
                String inLine = dis.readUTF();
                System.out.println(inLine);
                String outLine = scn.nextLine();
                dos.writeUTF(outLine);

                if(outLine.equalsIgnoreCase("Exit")){
                    System.out.println("Closing the connection "+ clientSocket);
                    clientSocket.close();
                    System.out.println("Connection Closed");
                    break;
                }
                    String received = dis.readUTF();
                    System.out.println(received);
            }
            dos.close();
            dis.close();
        } catch (Exception ex) {
            System.err.println("Error: " + ex.getMessage());
        }
    }
}