├── Constants.java             # Central application constants
├── app/
│   ├── web/                   # Controllers (Actions)
│   │   ├── base/              # Base action classes (FessBaseAction, FessAdminAction)
│   │   ├── admin/             # Admin controllers ({feature}/ with Action, Forms)
│   │   └── api/               # API controllers
│   ├── service/               # Business logic services

 * for API endpoints including authentication, message handling, and access control.
 *
 * This class extends FessBaseAction and provides specialized behavior for API requests,
 * including token-based authentication and JSON response handling.
 */
public abstract class FessApiAction extends FessBaseAction {

    /**
     * Default constructor.
     */
    public FessApiAction() {
        super();
    }

    /**