panel.addButton(btn);
panel.addListener(Events.BeforeSubmit, new Listener<FormEvent>() {
public void handleEvent(FormEvent formEvent) {
panel.mask(Messages.get("label.loading", "Loading..."));
}
});
panel.addListener(Events.Submit, new Listener<FormEvent>() {
public void handleEvent(FormEvent formEvent) {
String result = formEvent.getResultHtml();