code: public void run() throws MojoExecutionException {
      try {
        runMojo
            .getAppEngineFactory()
            .devServerRunSync()
            .run(configBuilder.buildRunConfiguration(processServices(), processProjectId()));
      } catch (AppEngineException ex) {
        throw new MojoExecutionException("Failed to run devappserver", ex);
      }
    }
docs: Run the dev appserver.