Java 架构：把复杂度关进边界里

// domain：业务规则，不依赖 Spring / JPA
public record Order(String id, long amount) {}

public interface OrderRepository {
    void save(Order order);
}

// application：用例编排，只依赖抽象
public class PlaceOrder {
    private final OrderRepository repo;

    public PlaceOrder(OrderRepository repo) {
        this.repo = repo;
    }

    public void handle(String id, long amount) {
        if (amount <= 0) throw new IllegalArgumentException("金额必须为正");
        repo.save(new Order(id, amount));
    }
}

// adapter：框架细节，放最外层
@RestController
public class OrderController {
    private final PlaceOrder placeOrder;

    public OrderController(PlaceOrder placeOrder) {
        this.placeOrder = placeOrder;
    }

    @PostMapping("/orders")
    public void create(@RequestParam String id, @RequestParam long amount) {
        placeOrder.handle(id, amount);
    }
}

order/
  domain/
  application/
  adapter/in/web/
  adapter/out/persistence/