Какво означава това предупреждение във Vaadin: Игнориране на RPC повикване за деактивиран конектор com.vaadin.ui.Window?

Опитах се да потърся в Google, за да намеря някои съвети и да разгледам уебсайта на Vaadin, но не намерих нищо свързано с този цар на проблема:

В конзолата, когато стартирам приложението, виждам това предупреждение няколко пъти:

Игнориране на RPC повикване за деактивиран конектор com.vaadin.ui.Window, caption=Надпис на прозореца

Използвам добавката Refresher, която анкетира сървъра ми на интервал от 2000 милисекунди. и добавката ICEPush, която прилага натискане към потребителския интерфейс на Vaadin.

Мисля, че това е свързано по някакъв начин с добавката Refresher, защото ако взаимодействам с компонент, който съм създал за тест (под кода), предупрежденията се добавят към конзолата.

Ето кода:

package com.example.events;

import java.util.ArrayList;
import java.util.List;

import com.github.wolfie.refresher.Refresher;
import com.vaadin.event.FieldEvents.BlurListener;
import com.vaadin.event.FieldEvents.FocusListener;
import com.vaadin.event.FieldEvents.TextChangeEvent;
import com.vaadin.event.FieldEvents.TextChangeListener;
import com.vaadin.event.LayoutEvents.LayoutClickNotifier;
import com.vaadin.ui.AbstractTextField.TextChangeEventMode;
import com.vaadin.ui.Button;

import com.vaadin.ui.Button.ClickEvent;
import com.vaadin.ui.Button.ClickListener;
import com.vaadin.ui.Component;
import com.vaadin.ui.Label;
import com.vaadin.ui.Layout;
import com.vaadin.ui.Notification;
import com.vaadin.ui.TextArea;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;
import com.vaadin.ui.Window;

public class Noticeboard extends VerticalLayout {

    /**
     * 
     */
    private static final long serialVersionUID = -6023888496081433464L;

    private static List<Note> notes = new ArrayList<Note>();
    private List<Window> windows = new ArrayList<Window>();
    private static int userCount;
    private int userId;
    private static int noteId;
    private Refresher refresher = new Refresher();
    private static final int UPDATE_INTERVAL = 2000;
    private Note currentlyFocusedNote;

    public class NoticeboardUpdater extends Thread {

        @Override
        public void run() {
            while (true) {
                try {
                    Thread.sleep(UPDATE_INTERVAL);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                getUI().getSession().getLockInstance().lock();
                try {
                    updateNoticeboard();
                } finally {
                    getUI().getSession().getLockInstance().unlock();
                }
            }
        }

    }

    public Noticeboard() {
        refresher.setRefreshInterval(UPDATE_INTERVAL);
        userId = ++userCount;
        setSpacing(true);
        setMargin(true);
        addComponent(new Label("Logged in as User " + userId));
        Button addNoteButton = new Button("Add note");

        addNoteButton.addClickListener(new ClickListener() {

            /**
             * 
             */
            private static final long serialVersionUID = -4927018162887570343L;

            @Override
            public void buttonClick(ClickEvent event) {
                Note note = new Note(++noteId);
                note.setCaption("Note " + note.getId());
                notes.add(note);

                Window window = createWindow(note);
                windows.add(window);

                UI.getCurrent().addWindow(window);
            }
        });

        addComponent(addNoteButton);
        addExtension(refresher);        
        new NoticeboardUpdater().start();
    }

    private Window createWindow(final Note note) {
        final Window window = new Window(note.getCaption());
        VerticalLayout layout = new VerticalLayout();
        layout.addComponent(createContentNote(note, window));
        window.setContent(layout);
        window.setWidth(300, Unit.PIXELS);
        window.setResizable(false);
        window.setPositionX(note.getPositionX());
        window.setPositionY(note.getPositionY());
        window.setData(note);
        window.addBlurListener(createBlurListener(window));
        window.addFocusListener(createFocusListener(window));

        LayoutClickNotifier mainLayout = (LayoutClickNotifier) getUI().getContent();
        mainLayout.addLayoutClickListener(e -> {
            if (note.isNoteFocusedWindow() || note.isNoteFocusedTextArea()) {               
                if (note.getLockedByUser() > -1 && note.getLockedByUser() == userId) {                  
                    unlockNote(getWindow(currentlyFocusedNote));
                    note.setNoteFocusedWindow(false);
                    note.setNoteBlurredWindow(false);
                    note.setNoteFocusedTextArea(false);
                    note.setNoteBlurredTextArea(false);                 

                    currentlyFocusedNote = null;
                }
            }
        });

        return window;
    }

    private TextArea createContentNote(final Note note, final Window window) {
        TextArea contentNote = new TextArea();
        contentNote.setSizeFull();
        contentNote.setValue(note.getText());
        contentNote.setImmediate(true);
        contentNote.setTextChangeEventMode(TextChangeEventMode.EAGER);
        contentNote.addBlurListener(createBlurListener(window));
        contentNote.addFocusListener(createFocusListener(window));
        contentNote.addTextChangeListener(new TextChangeListener() {

            /**
             * 
             */
            private static final long serialVersionUID = 8552875156973567499L;

            @Override
            public void textChange(TextChangeEvent event) {
                note.setText(event.getText());
            }
        });
        return contentNote;
    }

    private BlurListener createBlurListener(Window window) {
        return e -> {
            Component blurredComponent = e.getComponent();

            if (blurredComponent == window)  {
                currentlyFocusedNote.setNoteBlurredWindow(true);
            }
            else if (blurredComponent == (((Layout) window.getContent())).iterator().next()) {
                currentlyFocusedNote.setNoteBlurredTextArea(true);
            }

        };
    }

    private FocusListener createFocusListener(Window window) {
        return e -> {
            Component focusedComponent = e.getComponent();
            Note note = (Note) window.getData();

            if (currentlyFocusedNote != null && currentlyFocusedNote != note) {
                unlockNote(getWindow(currentlyFocusedNote));        
                currentlyFocusedNote.setNoteFocusedWindow(false);
                currentlyFocusedNote.setNoteBlurredWindow(false);
                currentlyFocusedNote.setNoteFocusedTextArea(false);
                currentlyFocusedNote.setNoteBlurredTextArea(false);
            }

            currentlyFocusedNote = note;
            if (focusedComponent == window) {
                Notification.show("Focused Note Window");
                currentlyFocusedNote.setNoteFocusedWindow(true);
            }
            else if (focusedComponent == (((Layout) window.getContent())).iterator().next()) {
                Notification.show("Focused Note TextArea");
                currentlyFocusedNote.setNoteFocusedTextArea(true);
            }

            if (currentlyFocusedNote.isNoteFocusedWindow() && currentlyFocusedNote.isNoteBlurredTextArea() || 
                currentlyFocusedNote.isNoteFocusedTextArea() && currentlyFocusedNote.isNoteBlurredWindow()) {
                // Lock is already set here, skipping
                return;
            }                       
            lockNote(window);
        };
    }

    private void lockNote(Window window) {
        Note note = (Note) window.getData();
        note.setLockedByUser(userId);
        String caption = "Locked by User " + userId;
        note.setCaption(caption);
        window.setCaption(caption);
    }

    private void unlockNote(Window window) {
        Note note = (Note) window.getData();
        note.setLockedByUser(-1);
        note.setPositionX(window.getPositionX());
        note.setPositionY(window.getPositionY());
        note.setCaption("Note " + note.getId());
        window.setCaption("Note " + note.getId());
    }

    private void updateNoticeboard() {
        for (Note note : notes) {
            Window window = getWindow(note);

            if (window == null) {
                window = createWindow(note);
                windows.add(window);
                UI.getCurrent().addWindow(window);
            }

            if (note.getLockedByUser() > -1) {
                if (note.getLockedByUser() != userId) {
                    // If the note is locked by another user, then we disable this window. 
                    window.setEnabled(false);

                    updateTextArea(window, note);                   
                    updateWindowPosition(window, note);
                }
                else {                  
                    // Otherwise the window is enabled.
                    window.setEnabled(true);
                    Note focusedNote = (Note) window.getData();

                    updateFocusedNotePosition(focusedNote, window);
                }
            }           
            else {
                window.setEnabled(true);
                updateTextArea(window, note);
                updateWindowPosition(window, note);
            }           
        }
    }

    private void updateTextArea(Window window, Note note) {
        Layout layout = (Layout) window.getContent();
        TextArea area = (TextArea) layout.iterator().next();
        area.setValue(note.getText());
    }

    private Window getWindow(Note note) {
        for (Window window : windows) {
            if (window.getData().equals(note))
                return window;
        }
        return null;
    }

    private void updateWindowPosition(Window window, Note note) {
        window.setPositionX(note.getPositionX());
        window.setPositionY(note.getPositionY());
        window.setCaption(note.getCaption());
    }

    private void updateFocusedNotePosition(Note focusedNote, Window window) {       
        focusedNote.setPositionX(window.getPositionX());
        focusedNote.setPositionY(window.getPositionY());
        focusedNote.setCaption(window.getCaption());
    }
}

И вътре в метода init на потребителския интерфейс просто използвам този клас Noticeboard:

@Override
protected void init(VaadinRequest request) {
    setContent(new Noticeboard());
}

Когато преместя прозорец, създаден с бутона „Добавяне на бележка“, или променя фокуса от прозорец на друг, получавам предупреждението.

Каква може да е причината за такъв проблем?

Знам, че кодът не е от по-добрите, той е само за да видите как се държат тези добавки на Vaadin.