TextArea Push Example

CallsView.java

public class CallsView extends HorizontalLayout implements MyListener {

    private TextArea textArea;

    public CallsView() {
        setSizeFull();
        textArea = new TextArea();
        textArea.setSizeFull();
        this.addComponent(textArea);
    }

    @Override
    public void attach() {
        super.attach();
        MyListeners.addListener(this);
    }

    @Override
    public void detach() {
        super.detach();
        MyListeners.removeListener(this);
    }

    @Override
    public void onNewText(String msg) {
        UI ui = getUI();
        ui.access(() -> {
            textArea.setValue(textArea.getValue()+"\n"+msg);
            ui.push();
        });
    }
}

MyListener.java

public interface MyListener {

    void onNewText(String msg);

}

MyListeners.java

public class MyListeners {

    private static CopyOnWriteArraySet<MyListener> listeners = new CopyOnWriteArraySet<>();

    public static void addListener(MyListener listener) {
        listeners.add(listener);
    }

    public static void removeListener(MyListener listener) {
        listeners.remove(listener);
    }

    static void sendText(String message) {
        listeners.forEach(runSafe(message));
    }

    private static Consumer<MyListener> runSafe(String message) {
        return listener -> {
            try {
                listener.onNewText(message);
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        };
    }
}

MyUI.java

@Theme("mytheme")
@Push(PushMode.MANUAL)
public class MyUI extends UI {

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        final VerticalLayout layout = new VerticalLayout();
        layout.setSizeFull();
        layout.addComponent(new CallsView());
        setContent(layout);
    }

    @WebServlet(urlPatterns = "/*", name =  "MyUIServlet", asyncSupported = true)
    @VaadinServletConfiguration(ui = MyUI.class, productionMode = false, widgetset = "AppWidgetset")
    public static class MyUIServlet extends VaadinServlet {
    }

    // http://localhost:8080/command?message=MyNewMessage
    @WebServlet(urlPatterns = "/command", name =  "MyCmdServlet", asyncSupported = true)
    public static class MyCommandServlet extends HttpServlet {

        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            for (int i = 0; i < 5; i++) {
                MyListeners.sendText(req.getParameter("message"));
            }
        }
    }
}