code: protected void closeServerSocket() {
      ServerSocket serverSocket = getServerSocket();
  
      if (!close(serverSocket)) {
        getLogger().warning(() -> String.format(
          "Failed to close ServerSocket bound to address [%s], listening on port [%d]",
            serverSocket.getInetAddress(), serverSocket.getLocalPort()));
      }
    }
docs: Closes the {@link ServerSocket} used by the {@link EchoServer} to receive {@link EchoClient} connections.
  
  @see #getServerSocket()