private final List<Thread> hooks = Lists.newArrayList();

    @Override
    synchronized void addShutdownHook(Thread hook) {
      hooks.add(hook);
    }

    synchronized void shutdown() throws InterruptedException {
      for (Thread hook : hooks) {
        hook.start();
      }
      for (Thread hook : hooks) {
        hook.join();
      }
    }
  }

                    // following code, but unfortunately the behavior of logging
                    // is undefined in shutdown hooks.
                    // This is because the logging code installs a shutdown hook of its
                    // own. See Cleaner class inside {@link LogManager}.
                    service.shutdown();

    private final List<Thread> hooks = Lists.newArrayList();

    @Override
    synchronized void addShutdownHook(Thread hook) {
      hooks.add(hook);
    }

    synchronized void shutdown() throws InterruptedException {
      for (Thread hook : hooks) {
        hook.start();
      }
      for (Thread hook : hooks) {
        hook.join();
      }
    }
  }

     * already have to deal with, thanks to DI frameworks that perform field and method injection,
     * frameworks like Android that define post-construct hooks like Activity.onCreate, etc.
     */

    @CheckForNull private ValueSetLink<K, V> predecessorInValueSet;
    @CheckForNull private ValueSetLink<K, V> successorInValueSet;

        try {
            return createProtwordsItem(this, form, hook);
        } catch (final ValidationErrorException e) {
            saveToken();
            throw e;
        }
    }

    public static OptionalEntity<ProtwordsItem> createProtwordsItem(final FessBaseAction action, final CreateForm form,
            final VaErrorHook hook) {

        }
        return OptionalEntity.empty();
    }

    protected OptionalEntity<StemmerOverrideItem> createStemmerOverrideItem(final CreateForm form, final VaErrorHook hook) {
        try {
            return createStemmerOverrideItem(this, form, hook);
        } catch (final ValidationErrorException e) {
            saveToken();
            throw e;
        }
    }

        try {
            return createKuromojiItem(this, form, hook);
        } catch (final ValidationErrorException e) {
            saveToken();
            throw e;
        }
    }

    public static OptionalEntity<KuromojiItem> createKuromojiItem(final FessBaseAction action, final CreateForm form,
            final VaErrorHook hook) {

    //

    // ===================================================================================
    //                                                                               Hook
    //                                                                              ======

    // ===================================================================================

    // Attribute
    //
    @Resource
    private UserService userService;

    // ===================================================================================
    // Hook
    // ======

    // ===================================================================================
    // Search Execute
    // ==============

    @Execute
    public HtmlResponse index() {

    }

    public static OptionalEntity<StopwordsItem> createStopwordsItem(final CreateForm form, final VaErrorHook hook) {
        return getEntity(form).map(entity -> {
            final String newInput = form.input;
            validateStopwordsString(newInput, "input", hook);
            entity.setNewInput(newInput);
            return entity;
        });
    }