vaadin Login Page SimpleLoginUI

Example

public class SimpleLoginUI extends UI {

@Override
protected void init(VaadinRequest request) {

    //
    // Create a new instance of the navigator. The navigator will attach
    // itself automatically to this view.
    //
    new Navigator(this, this);

    //
    // The initial log view where the user can login to the application
    //
    getNavigator().addView(SimpleLoginView.NAME, SimpleLoginView.class);//

    //
    // Add the main view of the application
    //
    getNavigator().addView(SimpleLoginMainView.NAME,
            SimpleLoginMainView.class);

    //
    // We use a view change handler to ensure the user is always redirected
    // to the login view if the user is not logged in.
    //
    getNavigator().addViewChangeListener(new ViewChangeListener() {

        @Override
        public boolean beforeViewChange(ViewChangeEvent event) {

            // Check if a user has logged in
            boolean isLoggedIn = getSession().getAttribute("user") != null;
            boolean isLoginView = event.getNewView() instanceof SimpleLoginView;

            if (!isLoggedIn && !isLoginView) {
                // Redirect to login view always if a user has not yet
                // logged in
                getNavigator().navigateTo(SimpleLoginView.NAME);
                return false;

            } else if (isLoggedIn && isLoginView) {
                // If someone tries to access to login view while logged in,
                // then cancel
                return false;
            }

            return true;
        }

        @Override
        public void afterViewChange(ViewChangeEvent event) {

        }
    });
}
}