Usando WebSockets

package org.acme.websockets;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import javax.enterprise.context.ApplicationScoped;
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import javax.websocket.Session;

@ServerEndpoint("/chat/{username}")         (1)
@ApplicationScoped
public class ChatSocket {

    Map<String, Session> sessions = new ConcurrentHashMap<>(); (2)

    @OnOpen
    public void onOpen(Session session, @PathParam("username") String username) {
        sessions.put(username, session);
    }

    @OnClose
    public void onClose(Session session, @PathParam("username") String username) {
        sessions.remove(username);
        broadcast("User " + username + " left");
    }

    @OnError
    public void onError(Session session, @PathParam("username") String username, Throwable throwable) {
        sessions.remove(username);
        broadcast("User " + username + " left on error: " + throwable);
    }

    @OnMessage
    public void onMessage(String message, @PathParam("username") String username) {
        if (message.equalsIgnoreCase("_ready_")) {
            broadcast("User " + username + " joined");
        } else {
            broadcast(">> " + username + ": " + message);
        }
    }

    private void broadcast(String message) {
        sessions.values().forEach(s -> {
            s.getAsyncRemote().sendObject(message, result ->  {
                if (result.getException() != null) {
                    System.out.println("Unable to send message: " + result.getException());
                }
            });
        });
    }

}

package org.acme.websockets;

import java.net.URI;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.TimeUnit;

import javax.websocket.ClientEndpoint;
import javax.websocket.ContainerProvider;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import io.quarkus.test.common.http.TestHTTPResource;
import io.quarkus.test.junit.QuarkusTest;

@QuarkusTest
public class ChatTest {

    private static final LinkedBlockingDeque<String> MESSAGES = new LinkedBlockingDeque<>();

    @TestHTTPResource("/chat/stu")
    URI uri;

    @Test
    public void testWebsocketChat() throws Exception {
        try (Session session = ContainerProvider.getWebSocketContainer().connectToServer(Client.class, uri)) {
            Assertions.assertEquals("CONNECT", MESSAGES.poll(10, TimeUnit.SECONDS));
            Assertions.assertEquals("User stu joined", MESSAGES.poll(10, TimeUnit.SECONDS));
            session.getAsyncRemote().sendText("hello world");
            Assertions.assertEquals(">> stu: hello world", MESSAGES.poll(10, TimeUnit.SECONDS));
        }
    }

    @ClientEndpoint
    public static class Client {

        @OnOpen
        public void open(Session session) {
            MESSAGES.add("CONNECT");
            // Send a message to indicate that we are ready,
            // as the message handler may not be registered immediately after this callback.
            session.getAsyncRemote().sendText("_ready_");
        }

        @OnMessage
        void message(String msg) {
            MESSAGES.add(msg);
        }

    }

}