GWT MessageBox Dialog

import java.util.Optional;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.event.dom.client.KeyCodes;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.ui.*;

public class InfoDialog extends DialogBox {
    protected final Widget widget;
    protected final Button btnClose = new Button("Close", (ClickHandler) e -> hide());
    protected Optional<Focusable> onCloseFocusedWidget = Optional.empty();

    public InfoDialog(String title, Widget widget) {
        this.widget = widget;

        final VerticalPanel mainPanel = new VerticalPanel();
        final Panel buttonsPanel = new HorizontalPanel();

        mainPanel.setHorizontalAlignment(VerticalPanel.ALIGN_CENTER);
        mainPanel.add(widget);
        mainPanel.add(new HTML("<hr/>"));
        mainPanel.add(buttonsPanel);

        buttonsPanel.setStyleName("buttons-panel");
        buttonsPanel.add(btnClose);

        setText(title);
        setWidget(mainPanel);
    }

    public InfoDialog withOnCloseFocusable(Focusable widget) {
        onCloseFocusedWidget = Optional.of(widget);
        return this;
    }

    public InfoDialog withButtonText(String text) {
        btnClose.setText(text);
        return this;
    }

    @Override
    public void show() {
        super.show();
        if (widget instanceof Focusable)
            ((Focusable) widget).setFocus(true);
    }

    @Override
    public void center() {
        super.center();
        if (widget instanceof Focusable)
            ((Focusable) widget).setFocus(true);
    }

    @Override
    public void hide() {
        super.hide();
        onCloseFocusedWidget.ifPresent(f -> f.setFocus(true));
    }

    @Override
    protected void onPreviewNativeEvent(Event.NativePreviewEvent event) {
        super.onPreviewNativeEvent(event);
        if (event.getTypeInt() == Event.ONKEYDOWN) {
            final int code = event.getNativeEvent().getKeyCode();
            switch (code) {
                case KeyCodes.KEY_ENTER:
                case KeyCodes.KEY_ESCAPE:
                    hide(); break;
            }
        }
    }
}



// example:
public static void showMessage(String title, String message) {
    new InfoDialog(title, new HTML(message)).center();
}