How to show a Vaadin Notification to the User from seperate Thread

Question

I have a Quartz Job which checks every 30 min if there is a software update available. This i trigger in the code below. But i get a Nullpointer at UI.getCurrent(). How can i make a Notification visible, independet on which page the user is?

@Service
@DisallowConcurrentExecution
public class SystemJobCheckForUpdates extends UI implements Job  {

@Override
public void execute(JobExecutionContext jobExecutionContext) throws JobExecutionException {
    UI.getCurrent().access(() -> {
        Notification.show("Update available");
    });
  }
}

Answer 1

The "problem" is, that the sheduler is not associated with a concrete UI instance.

You will either need to store the UI instance in a global variable or use some kind of broadcast / message bus for this.