SImpleLoginMainView

public class SimpleLoginMainView extends CustomComponent implements View {

public static final String NAME = "";

Label text = new Label();

Button logout = new Button("Logout", new Button.ClickListener() {

    @Override
    public void buttonClick(ClickEvent event) {

        // "Logout" the user
        getSession().setAttribute("user", null);

        // Refresh this view, should redirect to login view
        getUI().getNavigator().navigateTo(NAME);
    }
});

public SimpleLoginMainView() {
    setCompositionRoot(new CssLayout(text, logout));
}

@Override
public void enter(ViewChangeEvent event) {
    // Get the user name from the session
    String username = String.valueOf(getSession().getAttribute("user"));

    // And show the username
    text.setValue("Hello " + username);
}
}