private void logout() {
    btnLogin.setVisible(true);
    btnRegistration.setVisible(true);
    btnAdvertReg.setVisible(false);
    btnMyAccout.setVisible(false);
    btnLogout.setVisible(false);
    btnAdminAccount.setVisible(false);

    AccountView.setAvailability(false);
    AdvertRegView.setAvailability(false);
    LetterView.setAvailability(false);
    AdminView.setAvailability(false);

    try {
      VaadinSession.getCurrent().getLockInstance().lock();
      VaadinSession.getCurrent().setAttribute(CURRENTUSER.toString(), null);
    } finally {
      VaadinSession.getCurrent().getLockInstance().unlock();
    }
    userLabel.setValue("");
  }