Hook for a new `UI` starting in Vaadin 14

Question

The Navigation Lifecycle in the Vaadin 14 manual says:

It is also possible to register a standalone listener for this event using the addBeforeEnterListener(BeforeEnterListener) method in UI.

But in modern Vaadin with the routing feature, we are no longer supposed to be writing a UI subsclass. My rough understanding is that there is indeed a UI object automatically instantiated for us, and then routing automatically replaces the content within that UI object. So the existence of a UI object is supposed to be transparent to us programmers using Vaadin Flow.

➥ So what is the lifecycle hook on a new UI instance so I can write a user-authentication check as a BeforeEnterListener to work globally across all my @Route views?

Calling UI.getCurrent will not do, as I would need to call that from somewhere in my layouts, but I am trying to register a listener before my layouts exist.

Answer 1

To hook into UI init, there is the UIInitListener.

A UIInitListener can be used to receive an event each time a new UI has been created and initialized.

The ideal place to add UIInitListeners would be inside a VaadinServiceInitListener

E.g. with Springboot:

@Bean
VaadinServiceInitListener vaadinServiceInitListener() {
    return new VaadinServiceInitListener() {
        @Override
        public void serviceInit(ServiceInitEvent serviceInitEvent) {
            serviceInitEvent.getSource().addUIInitListener( initEvent -> System.out.println("UI Init for " + initEvent.getUI()));
        }
    };
}