code: public boolean setListenerURL(String listenerURL) {
      String newURL = _substitutor.replace(listenerURL);
      boolean changed = false;
      if (!_urlValidator.isValid(newURL)) {
        error("The Response Listener URL specified is invalid. Continuing with previous value.");
      } else {
        if (!newURL.equalsIgnoreCase(_listenerURL)) {
          _listenerURL = newURL;
          _listenerTarget = createListenerTarget(newURL);
          changed = true;
        }
      }
      return changed;
    }
docs: Sets the Listener URL. Checks to see if the URL is valid, or it does
  nothing.
  
  @param listenerURL new URL for the client listener
  @return if this actually changed the listener URL