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.docker;
  
  import java.util.Optional;
  import java.util.logging.Logger;
  import org.openqa.selenium.internal.Require;
  import org.openqa.selenium.remote.http.HttpHandler;
  
  public class Docker {
  
    private static final Logger LOG = Logger.getLogger(Docker.class.getName());
    protected final HttpHandler client;
    private volatile Optional<DockerProtocol> dockerClient;
  
    public Docker(HttpHandler client) {
      this.client = Require.nonNull("HTTP client", client);
      this.dockerClient = Optional.empty();
    }
  
    public boolean isSupported() {
      return getDocker().isPresent();
    }
  
    public String getVersion() {
      return getDocker().map(DockerProtocol::version).orElse("unsupported");
    }
  
    public Image getImage(String name) {
      Require.nonNull("Image name to get", name);
  
      LOG.info("Obtaining image: " + name);
  
      return getDocker()
          .map(protocol -> protocol.getImage(name))
          .orElseThrow(() -> new DockerException("Unable to get image " + name));
    }
  
    public Container create(ContainerConfig config) {
      Require.nonNull("Container config", config);
  
      LOG.fine("Creating image from " + config);
  
      return getDocker()
          .map(protocol -> protocol.create(config))
          .orElseThrow(() -> new DockerException("Unable to create container: " + config));
    }
  
    public Optional<ContainerInfo> inspect(ContainerId id) {
      Require.nonNull("Container id", id);
  
      LOG.fine("Inspecting container with id: " + id);
  
      if (!getDocker().map(protocol -> protocol.isContainerPresent(id)).orElse(false)) {
        return Optional.empty();
      }
  
      return Optional.of(
          getDocker()
              .map(protocol -> protocol.inspectContainer(id))
              .orElseThrow(() -> new DockerException("Unable to inspect container: " + id)));
    }
  
    private Optional<DockerProtocol> getDocker() {
      if (dockerClient.isPresent()) {
        return dockerClient;
      }
  
      synchronized (this) {
        if (!dockerClient.isPresent()) {
          dockerClient = new VersionCommand(client).getDockerProtocol();
        }
      }
  
      return dockerClient;
    }
  }
  