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---
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 similiarly for `Page`. For instance adding a browser window
resize listener can be added like this:
[source,java]
....
javaPage.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).
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