code: public void open() throws IOException
      {
          if (_listen == null)
          {
              _listen = newServerSocket(_address, _acceptQueueSize);
  
              if (_address == null)
                  _address = new InetAddrPort(_listen.getInetAddress(), _listen.getLocalPort());
              else
              {
                  if (_address.getInetAddress() == null)
                          _address.setInetAddress(_listen.getInetAddress());
                  if (_address.getPort() == 0) _address.setPort(_listen.getLocalPort());
              }
  
              _soTimeOut = getMaxIdleTimeMs();
              if (_soTimeOut >= 0) _listen.setSoTimeout(_soTimeOut);
          }
      }
docs: Open the server socket. This method can be called to open the server socket in advance of
  starting the listener. This can be used to test if the port is available.
  
  @exception IOException if an error occurs