Finding the current root and application

There are many cases where you need a reference to the active Application or Root, 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 Root but Vaadin also offers an easier way through two static methods:

Root.getCurrent()
Application.getCurrent()

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

Button helloButton = new Button("Say Hello");
helloButton.addListener(new ClickListener() {
  public void buttonClick(ClickEvent event) {
    Notification.show("This Root is " + Root.getCurrent().getClass().getSimpleName());
  }
});

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

public void buttonClick(ClickEvent event) {
  String msg = "Running in ";
  msg += Application.getCurrent().isProductionMode() ?
    "production" : "debug";
  msg += " mode";
  Notification.show(msg);
}

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