@SuppressWarnings("FutureReturnValueIgnored")
  private Void listen() throws IOException {
    serverStarted.release();
    for (int i = 0; i < numThreads; i++) {
      Socket socket = serverSocket.accept();
      executorService.submit(() -> serveResponses(socket));
    }
    return null;
  }
Simple local web server for testing.
jib-core/src/test/java/com/google/cloud/tools/jib/http/TestWebServer.java