Real time notifications in spring boot web socket

Question

In my application, I need to send real time notifications to a specific user. My WebSocketConfig class is as below,

    @Configuration
    @EnableWebSocketMessageBroker
    public class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer {
        @Override
        public void registerStompEndpoints(StompEndpointRegistry stompEndpointRegistry) {
            stompEndpointRegistry.addEndpoint("/websocket-example")
                    .withSockJS();
        }

        @Override
        public void configureMessageBroker(MessageBrokerRegistry registry) {
            registry.enableSimpleBroker("/topic");
    }
}

Most of the time information will be sent by the server side. So I have not set the application destination.

In the client side, I am subscribing to the destination '/topic/user`,

function connect() {
    var socket = new SockJS('/websocket-example');
    stompClient = Stomp.over(socket);
    stompClient.connect({}, function (frame) {
        setConnected(true);
        console.log('Connected: ' + frame);
        stompClient.subscribe('/topic/user', function (greeting) {
//            showGreeting(JSON.parse(greeting.body).content);
console.log("Received message through WS");
        });
    });
}

In one of my RestController I have a method which broadcasts the message to all connected clients.

    @GetMapping("/test")
    public void test()
    {
        template.convertAndSend("/topic/user", "Hurray");
    }

Until this part everything works fine. I receive the message and is logging to the console.

Now If I want to send the notification only to specific users, I have to use template.convertAndSendToUser(String user, String destination, String message). But I am not understanding what I should pass to the user parameter. Where and when will I get the user?

I went through couple of questions related to this, but I am not understanding the concepts clearly.

Answer 1

Before sending any messages to a user you need to authenticate it by the server first. There are different ways for doing this. Spring Security is a key phrase here

https://docs.spring.io/spring-security/site/docs/current/guides/html5/helloworld-boot.html

When authentication is completed you can simply get user name by calling:

Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
String currentPrincipalName = authentication.getName();

https://www.baeldung.com/get-user-in-spring-security