code: public void deploy() throws MojoExecutionException {
      stager.stage();
  
      DeployConfiguration config =
          configBuilder.buildDeployConfiguration(ImmutableList.of(deployMojo.getStagingDirectory()));
  
      try {
        deployMojo.getAppEngineFactory().deployment().deploy(config);
      } catch (AppEngineException ex) {
        throw new MojoExecutionException("App Engine application deployment failed", ex);
      }
    }
docs: Deploy a single application (and no project configuration).