Не получается выполнить 7-й пункт "Если какая-то проверка не прошла, заново запросить имя клиента"

package com.javarush.task.task30.task3008;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class Server {
    private static Map<String, Connection> connectionMap = new ConcurrentHashMap<>();

    public static void main(String[] args) {
        ConsoleHelper.writeMessage("Input port:");
        try (ServerSocket serverSocket = new ServerSocket(ConsoleHelper.readInt())) {
            ConsoleHelper.writeMessage("Server is ON.");
            while (true) {
                new Handler(serverSocket.accept()).start();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void sendBroadcastMessage(Message message) {
        for (String name : connectionMap.keySet()) {
            try {
                connectionMap.get(name).send(message);
            } catch (IOException e) {
                ConsoleHelper.writeMessage(String.format("Can't send the message to %s", name));
            }
        }
    }

    private static class Handler extends Thread {
        Socket socket;

        public Handler(Socket socket) {
            this.socket = socket;
        }

        private String serverHandshake(Connection connection) throws IOException, ClassNotFoundException {
            Message request = new Message(MessageType.NAME_REQUEST);

            Message answer;

            do {
                connection.send(request);
                answer = connection.receive();
            }
            while (answer.getType() != MessageType.USER_NAME && answer.getData() == null && !connectionMap.containsKey(answer.getData()));

            connectionMap.put(answer.getData(), connection);
            connection.send(new Message(MessageType.USER_ADDED));

            return answer.getData();
        }
    }
}