When to use this skill
Use this skill whenever the user wants to:
- Structure an application following Clean Architecture layers (Entities, Use Cases, Interface Adapters, Frameworks)
- Enforce the dependency rule: inner layers never depend on outer layers
- Organize project packages and define clear test boundaries
- Combine Clean Architecture with Domain-Driven Design patterns
How to use this skill
Workflow
- Define Entities (innermost layer) containing enterprise-wide business rules
- Define Use Cases (application layer) containing application-specific business logic
- Create Interface Adapters (presenters, gateways) that convert data between layers
- Implement Frameworks (outermost layer) for web, database, and UI concerns
Layer Structure
com.example.app/
├── entity/ # Entities — business rules, no dependencies
├── usecase/ # Use Cases — application logic, depends only on entity
│ ├── port/ # Input/output port interfaces
│ └── interactor/ # Use case implementations
├── adapter/ # Interface Adapters — presenters, gateways
│ ├── controller/ # Web controllers
│ ├── presenter/ # Response formatting
│ └── gateway/ # Gateway implementations
└── framework/ # Frameworks — DB, web server, external APIs
├── web/
└── persistence/Use Case Example
// Use case port (input boundary)
public interface CreateOrderUseCase {
OrderOutput execute(CreateOrderInput input);
}
// Use case interactor
public class CreateOrderInteractor implements CreateOrderUseCase {
private final OrderGateway orderGateway;
private final PaymentGateway paymentGateway;
public CreateOrderInteractor(OrderGateway orderGateway, PaymentGateway paymentGateway) {
this.orderGateway = orderGateway;
this.paymentGateway = paymentGateway;
}
@Override
public OrderOutput execute(CreateOrderInput input) {
Order order = Order.create(input.getItems());
paymentGateway.charge(order.totalAmount());
orderGateway.save(order);
return OrderOutput.from(order);
}
}Gateway Interface (defined in Use Case layer)
public interface OrderGateway {
void save(Order order);
Optional<Order> findById(String id);
}Best Practices
- Concentrate business rules in Entities and Use Cases; avoid placing business logic in controllers or database layers
- Use interfaces to isolate I/O; this makes the core easy to replace and test
- Entities and Use Cases map naturally to DDD aggregates and domain services
- Test core layers with unit tests; test outer layers with integration or E2E tests
Resources
- Clean Architecture by Robert C. Martin
- https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html
Keywords
clean architecture, dependency rule, use case, entity, interface adapter, gateway, layer separation, DDD, testability