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SKILL.md
npx skills add gentleman-programming/gentleman-skills --skill hexagonal-architecture-layers-java
Hexagonal architecture layering for Java services with strict boundaries. Trigger: When structuring Java apps by Domain/Application/Infrastructure, or refactoring toward clean architecture.
npx skills add gentleman-programming/gentleman-skills --skill hexagonal-architecture-layers-java
Load this skill when:
Domain has no framework annotations, no persistence concerns, and no I/O.
Application defines use cases and ports, calling domain logic and delegating I/O to ports.
Infrastructure implements ports and wires adapters (controllers, repositories, clients).
| Task | Pattern |
|---|---|
| Persist domain data | Define output port in application, implement in infrastructure |
| Expose use case | Define input port and service in application |
| Keep domain pure | No annotations, no I/O, no framework imports |
package com.acme.order.application.port;
import com.acme.order.domain.Order;
import com.acme.order.domain.OrderId;
public interface OrderRepositoryPort {
OrderId nextId();
void save(Order order);
}package com.acme.order.application.usecase;
import com.acme.order.application.port.OrderRepositoryPort;
import com.acme.order.domain.Order;
import com.acme.order.domain.OrderId;
import com.acme.order.domain.Money;
public interface PlaceOrderUseCase {
OrderId place(Money total);
}
public final class PlaceOrderService implements PlaceOrderUseCase {
private final OrderRepositoryPort repository;
public PlaceOrderService(OrderRepositoryPort repository) {
this.repository = repository;
}
@Override
public OrderId place(Money total) {
OrderId id = repository.nextId();
Order order = new Order(id, total);
repository.save(order);
return id;
}
}package com.acme.order.infrastructure.persistence;
import com.acme.order.application.port.OrderRepositoryPort;
import com.acme.order.domain.Order;
import com.acme.order.domain.OrderId;
import org.springframework.stereotype.Repository;
@Repository
public final class OrderJpaAdapter implements OrderRepositoryPort {
private final SpringOrderRepository repository;
private final OrderMapper mapper;
public OrderJpaAdapter(SpringOrderRepository repository, OrderMapper mapper) {
this.repository = repository;
this.mapper = mapper;
}
@Override
public OrderId nextId() {
return new OrderId(java.util.UUID.randomUUID().toString());
}
@Override
public void save(Order order) {
repository.save(mapper.toEntity(order));
}
}// BAD: domain tied to JPA
@jakarta.persistence.Entity
public class Order {
@jakarta.persistence.Id
private String id;
}// BAD: domain depends on Spring repository
public class Order {
private final SpringOrderRepository repository;
}