code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC licenses this file
  // to you under the Apache License, Version 2.0 (the
  // "License"); you may not use this file except in compliance
  // with the License.  You may obtain a copy of the License at
  //
  //   http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing,
  // software distributed under the License is distributed on an
  // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  // KIND, either express or implied.  See the License for the
  // specific language governing permissions and limitations
  // under the License.
  
  package org.openqa.selenium.testing.drivers;
  
  import static org.openqa.selenium.remote.http.Contents.string;
  
  import java.io.IOException;
  import java.io.UncheckedIOException;
  import java.net.URL;
  import java.time.Duration;
  import java.util.Map;
  import java.util.function.Supplier;
  import org.openqa.selenium.Capabilities;
  import org.openqa.selenium.WebDriver;
  import org.openqa.selenium.firefox.FirefoxOptions;
  import org.openqa.selenium.json.Json;
  import org.openqa.selenium.remote.LocalFileDetector;
  import org.openqa.selenium.remote.RemoteWebDriver;
  import org.openqa.selenium.remote.http.HttpClient;
  import org.openqa.selenium.remote.http.HttpMethod;
  import org.openqa.selenium.remote.http.HttpRequest;
  import org.openqa.selenium.remote.http.HttpResponse;
  import org.openqa.selenium.support.ui.FluentWait;
  import org.openqa.selenium.support.ui.Wait;
  
  class GridSupplier implements Supplier<WebDriver> {
  
    private static OutOfProcessSeleniumServer hub;
    private static OutOfProcessSeleniumServer node;
    private static volatile boolean started;
  
    private final Capabilities desired;
  
    public GridSupplier(Capabilities desired) {
      this.desired = desired;
    }
  
    @Override
    public WebDriver get() {
      if (desired == null || !Boolean.getBoolean("selenium.browser.grid")) {
        return null;
      }
  
      if (!started) {
        startServers();
      }
  
      RemoteWebDriver driver = new RemoteWebDriver(hub.getWebDriverUrl(), desired);
      driver.setFileDetector(new LocalFileDetector());
      return driver;
    }
  
    private synchronized void startServers() {
      if (started) {
        return;
      }
  
      try {
        hub = new OutOfProcessSeleniumServer().start("-role", "hub");
  
        URL hubUrl = hub.getWebDriverUrl();
        hubUrl = new URL(hubUrl.getProtocol(), hubUrl.getHost(), hubUrl.getPort(), hubUrl.getFile());
  
        node =
            new OutOfProcessSeleniumServer().start("-role", "node", "-hub", String.valueOf(hubUrl));
      } catch (IOException e) {
        throw new UncheckedIOException(e);
      }
  
      // Keep polling the status page of the hub until it claims to be ready
      try (HttpClient client =
          HttpClient.Factory.createDefault().createClient(hub.getWebDriverUrl())) {
        Json json = new Json();
        Wait<HttpClient> wait =
            new FluentWait<>(client)
                .ignoring(RuntimeException.class)
                .withTimeout(Duration.ofSeconds(30));
        wait.until(
            c -> {
              HttpRequest req = new HttpRequest(HttpMethod.GET, "/status");
              HttpResponse response = c.execute(req);
              Map<?, ?> value = json.toType(string(response), Map.class);
  
              return Boolean.TRUE.equals(((Map<?, ?>) value.get("value")).get("ready"));
            });
      }
  
      started = true;
    }
  
    public static void main(String[] args) {
      System.setProperty("selenium.browser.grid", "true");
      WebDriver driver = new GridSupplier(new FirefoxOptions()).get();
      driver.get("http://www.google.com");
    }
  }
  