Quero enviar uma notificação para um cliente específico.

por exemplo, nome de usuário usuário

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfiguration extends
    AbstractWebSocketMessageBrokerConfigurer {

        @Override
        public void registerStompEndpoints(StompEndpointRegistry stompEndpointRegistry) {
            stompEndpointRegistry.addEndpoint("/socket")
                    .setAllowedOrigins("*")
                    .withSockJS();
        }

        @Override
        public void configureMessageBroker(MessageBrokerRegistry registry) {
            registry.enableSimpleBroker("/topic", "/queue");
            registry.setApplicationDestinationPrefixes("/app");

        }

Controlador

@GetMapping("/notify")
public String getNotification(Principal principal) {
    String username = "user";

    notifications.increment();
    logger.info("counter" + notifications.getCount() + "" + principal.getName());
    //  logger.info("usersend:"+sha.getUser().getName()) ; //user

    template.convertAndSendToUser(principal.getName(), "queue/notification", notifications);

    return "Notifications successfully sent to Angular !";
}

Lado do Cliente

Serviço Angular

connect() {
    let socket = new SockJs(`api/socket`);

    let stompClient = Stomp.over(socket);

    return stompClient;
}

Componente angular

 let stompClient = this.webSocketService.connect();

     stompClient.connect({}, frame => {

      stompClient.subscribe('/user/queue/notification', notifications => {
               console.log('test'+notifications)
          this.notifications = JSON.parse(notifications.body).count;

      })     });

Pesquisei muitas outras perguntas e tentei, mas nenhuma delas funcionou para mim, por exemploaqui respondida por Thanh Nguyen Van eaqui

Console

 Opening Web Socket...
    stomp.js:134 Web Socket Opened...
    stomp.js:134 >>> CONNECT
    accept-version:1.1,1.0
    heart-beat:10000,10000


    stomp.js:134 <<< CONNECTED
    version:1.1
    heart-beat:0,0


    stomp.js:134 connected to server undefined
    reminder.component.ts:18 test callsed
    stomp.js:134 >>> SUBSCRIBE
    id:sub-0
    destination:/user/queue/notification

desde já, obrigado .