if(vectorLayer.getFeaturesLoadedListeners() != null
&& vectorLayer.getFeaturesLoadedListeners().size() > 0) {
// add a behavior to be notified when new features are loaded
VectorFeaturesLoadedListener vectorFeatureLoadedListener =
new VectorFeaturesLoadedListener(vectorLayer) {
@Override
public void handleDataLoaded(AjaxRequestTarget target) {
vectorLayer.notifyFeaturesLoadedListeners(target);
}