Repeater repeater = (Repeater)form.getChild("contacts");
repeater.addRow();
Field field = (Field)repeater.getWidget(0, "firstname");
field.setValue("Jules");
repeater.addRow();
field = (Field)repeater.getWidget(1, "firstname");
field.setValue("Lucien");
Request request = ObjectModelHelper.getRequest(objectModel);
request.setAttribute(formAttribute, form);