vaadin-framework/documentation/articles/FindingTheCurrentUIAndPageAndVaadinSession.asciidoc

---
title: Finding The Current UI And Page And Vaadin Session
order: 18
layout: page
---

[[finding-the-current-ui-and-page-and-vaadin-session]]
= Finding the current UI and page and vaadin session

There are many cases where you need a reference to the active `UI`, `Page`
or `VaadinServiceSession`, for instance for showing notifications in a
click listener. It is possible to get a reference to the component from
the event and then a reference from the component to the UI but Vaadin
also offers an easier way through two static methods:

[source,java]
....
UI.getCurrent()
Page.getCurrent()
VaadinSession.getCurrent()
....

For example when you want to show the name of the current UI class:

[source,java]
....
Button helloButton = new Button("Say Hello");
    helloButton.addClickListener(new ClickListener() {
        @Override
        public void buttonClick(ClickEvent event) {
            Notification.show("This UI is "
                    + UI.getCurrent().getClass().getSimpleName());
        }
    });
....

Similarly for `VaadinServiceSession`, for instance to find out if the
application is running in production mode:

[source,java]
....
public void buttonClick(ClickEvent event) {
    String msg = "Running in ";
    msg += VaadinSession.getCurrent().getConfiguration()
            .isProductionMode() ? "production" : "debug";
    Notification.show(msg);
}
....

And finally similarly for `Page`. For instance adding a browser window
resize listener can be added like this:

[source,java]
....
Page.getCurrent().addBrowserWindowResizeListener(
  new Page.BrowserWindowResizeListener() {
    @Override
    public void browserWindowResized(BrowserWindowResizeEvent event) {
      Notification.show("Browser resized to " + event.getWidth() + "x" + event.getHeight());
    }
});
....

*Note* that these are based on `ThreadLocal` so they won't work in a
background thread (or otherwise outside the standard request scope).