# CLAUDE.md — system-common

Shared Java library used by all backend modules.

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## Service layer pattern

Two base classes defined here:

| Base | Purpose |
|---|---|
| `CrudService<Dao, Entity, DTO>` | Generic CRUD: `page()`, `get()`, `save()`, `update()`, `delete()` |
| `BaseService<Dao>` | Lighter base without DTO generic |

These are used by all service implementations in `system-admin` and other modules. See `system-admin/CLAUDE.md` for the full module convention.

## i18n validation messages

Located at `src/main/resources/i18n/validation.properties`. Hibernate Validator messages used by `@RestControllerAdvice` exception handler in `system-admin`. Error codes follow `int` scheme: 5 digits, first 2 = module, last 3 = business (e.g. `10001`-`10029`).