Get principal inside scheduled method for Spring Websocket messaging - spring

Question

Want to send notifications to specific client with websockets. Have a scheduled task for sending notifications, but cannot get Principal inside that task. Found this post, but as I know Spring scheduled methods must be parameter-free.
#Scheduled(fixedDelay=5000)
public void sendMessages(Principal principal)
messagingTemplate
.convertAndSendToUser(principal.getName(), "/queue/horray", "Horray, " + principal.getName() + "!");
}
Is this possible? How can I get websocket principal within scheduled method?

Answer 1

You can not get principal in a scheduled method , because the method call is not initiated by user.
You can follow this approach:
1) Create a websocket end point "/app/events"
2) Let all users to subscribe to that end point
3) Get all the userids you want to send notifications
4) Send notification to single user
simpMessagingTemplate.convertAndSendToUser("userId", "/app/events", "messageEntity");
userId: can be actual user id if authenticated or it can be websocket session id.

Answer 2

I wrote a workaround for this situation. At first I create a listener for websockets events. In case of subscription request I keep the userId from the request and keep in a ConcurrentHashMap. On the other hand when client disconnects or send unsubscribe request I remove his userId from that Map.
My Listener class:
#Service
public class MyEventListener {
#Autowired
private NotificationPublisher notificationPublisher;
#EventListener({SessionSubscribeEvent.class})
public void onWebSocketSubscribeEvent(SessionSubscribeEvent event) {
notificationPublisher.subscribedUsers.put(event.getUser().getName(), Calendar.getInstance().getTimeInMillis());
}
#EventListener({SessionUnsubscribeEvent.class})
public void onWebSocketUnsubscribeEvent(SessionUnsubscribeEvent event) {
notificationPublisher.subscribedUsers.remove(event.getUser().getName());
}
#EventListener({SessionDisconnectEvent.class})
public void onWebSocketDisconnectEvent(SessionDisconnectEvent event) {
notificationPublisher.subscribedUsers.remove(event.getUser().getName());
}
}
Notification publisher class where actual job is running:
public class NotificationPublisher {
public final Map<String, Long> subscribedUsers = new ConcurrentHashMap<>();
#Autowired
private SimpMessagingTemplate messagingTemplate;
#Autowired
private MyService myService;
#Value("${task.notifications.publisher.websocket_timeout_seconds}")
private int websocketSessionTimeout;
public void sendDataUpdates() {
SocketResponseCount count = null;
for(String key: subscribedUsers.keySet()) {
long subscribeTime = subscribedUsers.get(key);
if(Calendar.getInstance().getTimeInMillis() - subscribeTime > websocketSessionTimeout*1000) {
subscribedUsers.remove(key);
continue;
}
count = myService.getNotificationsCount(key);
this.messagingTemplate.convertAndSendToUser(key, "/queue/publish",count);
}
}
}
Maybe it will help someone

Answer 3

my solution: I get all user sessions
#Autowired
private SimpMessagingTemplate template;
#Autowired
private MyRepository myRepository;
#Autowired
private SessionRegistry sessionRegistry;
#Scheduled(fixedRate = 5000)
public void greeting() {
List<SessionInformation> activeSessions = new ArrayList<>();
for (Object principal : sessionRegistry.getAllPrincipals() )
{
activeSessions.addAll( sessionRegistry.getAllSessions( principal, false ) );
}
for (SessionInformation session : activeSessions )
{
Object principalObj = session.getPrincipal();
if ( principalObj instanceof CurrentUser)
{
CurrentUser user = (CurrentUser) principalObj;
this.template.convertAndSendToUser(user.getUsername().toUpperCase(),"/queue/reply2",myRepository.findAll());
}
}
}