class FileUriFormatter

class FileUriFormatter extends BaseFieldFileFormatterBase {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        $settings = parent::defaultSettings();
        $settings['file_download_path'] = FALSE;
        return $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $form = parent::settingsForm($form, $form_state);
        $form['file_download_path'] = [
            '#title' => $this->t('Display the file download URI'),
            '#type' => 'checkbox',
            '#default_value' => $this->getSetting('file_download_path'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function viewValue(FieldItemInterface $item) {
        $value = $item->value;
        if ($this->getSetting('file_download_path')) {
            $value = $this->fileUrlGenerator
                ->generateString($value);
        }
        return $value;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function isApplicable(FieldDefinitionInterface $field_definition) {
        return parent::isApplicable($field_definition) && $field_definition->getName() === 'uri';
    }

}