code: public static void pullImage(String imageTag, String username, String password, String host) throws IOException {
          final AuthConfig authConfig = new AuthConfig();
          authConfig.withUsername(username);
          authConfig.withPassword(password);
  
          DockerClient dockerClient = null;
          try {
              dockerClient = getDockerClient(host);
              dockerClient.pullImageCmd(imageTag).withAuthConfig(authConfig).exec(new PullImageResultCallback()).awaitSuccess();
          } finally {
              closeQuietly(dockerClient);
          }
      }
docs: Pull docker image using the docker java client.
  
  @param imageTag
  @param username
  @param password
  @param host