MessageBoardEndpoint.java

@ServerEndpoint(
        value = "/websocket",
        encoders = { UppercaseEncoder.class })
public class MessageBoardEndpoint {
  
    @Inject
    private MessageQueue messageQueue;
  
    @OnMessage
    public void onMessage(Session session, String message) {
        if (message.equals("SEND")) {
            while (!messageQueue.isEmpty()) {
              session.getBasicRemote()
                     .sendObject(messageQueue.pop());
            }
        }
    }
}