code: public void validateAppEngineJavaComponents()
        throws AppEngineJavaComponentsNotInstalledException {
      if (!Files.isDirectory(getAppEngineSdkForJavaPath())) {
        throw new AppEngineJavaComponentsNotInstalledException(
            "Validation Error: Java App Engine components not installed."
                + " Fix by running 'gcloud components install app-engine-java' on command-line.");
      }
      if (!Files.isRegularFile(jarLocations.get(JAVA_TOOLS_JAR))) {
        throw new AppEngineJavaComponentsNotInstalledException(
            "Validation Error: Java Tools jar location '"
                + jarLocations.get(JAVA_TOOLS_JAR)
                + "' is not a file.");
      }
    }
docs: Checks whether the App Engine Java components are installed in the expected location in the
  Cloud SDK.
  
  @throws AppEngineJavaComponentsNotInstalledException when the App Engine Java components are
  not installed in the Cloud SDK