Vaadin

package com.example.ramen;

import javax.servlet.annotation.WebServlet;

import com.vaadin.annotations.Theme;
import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.server.VaadinRequest;
import com.vaadin.server.VaadinServlet;
import com.vaadin.ui.Button;
import com.vaadin.ui.Button.ClickEvent;
import com.vaadin.ui.Label;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;

@SuppressWarnings("serial")
@Theme("ramen")
public class RamenUI extends UI {

    @WebServlet(value = "/*", asyncSupported = true)
	@VaadinServletConfiguration(productionMode = false, ui = RamenUI.class)
	public static class Servlet extends VaadinServlet {
	}

	@Override
	protected void init(VaadinRequest request) {
		final VerticalLayout layout = new VerticalLayout();
		layout.setMargin(true);
		setContent(layout);

		Button button = new Button("ボタン");
		button.addClickListener(new Button.ClickListener() {
			public void buttonClick(ClickEvent event) {
				layout.addComponent(new Label("あdg"));
			}
		});
		layout.addComponent(button);
	}

}