show message when user enter the application (only once per session)

Vaadin 6 / 7 / 8 Framework UI
1

Hi,

I want to show a message to the user when he enter the application. But the message should be shown only once per session.
What is the best way to do that?

thanks a lot

2

One way is to store a boolean flag in VaadinSession that indicates whether or not the message was shown to the user. Then add a UIInitListener that would check this boolean flag and display the message if appropriate.

Here is the code in a Vaadin + Spring project:

@SpringComponent
public class ApplicationServiceInitListener implements VaadinServiceInitListener {

    @Override
    public void serviceInit(ServiceInitEvent serviceInitEvent) {
        
        serviceInitEvent.getSource().addSessionInitListener(initEvent -> {
            initEvent.getSession().setAttribute("isMsgDisplayed", Boolean.FALSE);
        });

        serviceInitEvent.getSource().addUIInitListener(event -> {
            VaadinSession currSession = VaadinSession.getCurrent();
            if (!(boolean) currSession.getAttribute("isMsgDisplayed")) {
                UI ui = event.getUI();
                ui.addBeforeEnterListener(beforeEvent -> {

                    Dialog d = new Dialog(new Span("A one time message"));
                    d.open();
                });

                currSession.setAttribute("isMsgDisplayed", Boolean.TRUE);
            }
        });        
    }
}

In a plain Java project (non-Spring), this class should be registered as a provider via Java SPI loading facility as described here: https://vaadin.com/docs/v14/flow/advanced/tutorial-service-init-listener.html