code: public void join()
          throws InterruptedException
      { 
          for (int l=0;l<_listeners.size();l++)
          {
              HttpListener listener =(HttpListener)_listeners.get(l); 
              if (listener.isStarted() && listener instanceof ThreadPool)
              {
                  ((ThreadPool)listener).join();
              }
          }
      }
docs: Join the listeners.
  Join all listeners that are instances of ThreadPool.
  @exception InterruptedException