Domain、BO、BIZ 三层的协作关系

电商、银行、医疗三个领域的经典分层案例，展示 domain、bo、biz 三层的协作关系：

‌案例1：电商订单系统‌

‌1. Domain层（领域模型）

// domain/entity/Order.java
public class Order {
    private String orderId;
    private List<OrderItem> items;
    private OrderStatus status;

    // 领域行为：计算订单总价
    public BigDecimal calculateTotal() {
        return items.stream()
            .map(item -> item.getPrice().multiply(item.getQuantity()))
            .reduce(BigDecimal.ZERO, BigDecimal::add);
    }
}

‌2. BO层（业务对象）

// bo/OrderBO.java
public class OrderBO {
    private Order order;
    private InventoryService inventoryService;

    // 业务逻辑：校验库存并预留
    public void reserveInventory() {
        if (!inventoryService.checkStock(order.getItems())) {
            throw new BusinessException("库存不足");
        }
    }
}

‌3. Biz层（业务服务）

// biz/OrderService.java
public class OrderService {
    public void createOrder(OrderCreateDTO dto) {
        OrderBO orderBO = new OrderBO(convertToOrder(dto));
        orderBO.reserveInventory();  // 调用BO处理业务规则
        paymentService.charge(orderBO.getOrder());  // 协调第三方支付
    }
}

‌案例2：银行转账系统‌

‌1. Domain层

// domain/entity/Account.java
public class Account {
    private String accountId;
    private BigDecimal balance;

    // 领域行为：扣款
    public void debit(BigDecimal amount) {
        if (balance.compareTo(amount) < 0) {
            throw new InsufficientBalanceException();
        }
        this.balance = balance.subtract(amount);
    }
}

‌2. BO层

// bo/TransferBO.java
public class TransferBO {
    private Account source;
    private Account target;

    // 业务逻辑：执行双账户原子操作
    public void executeTransfer(BigDecimal amount) {
        source.debit(amount);
        target.credit(amount);  // 省略credit方法实现
    }
}

‌3. Biz层

// biz/TransferService.java
public class TransferService {
    @Transactional
    public void transfer(TransferRequestDTO dto) {
        TransferBO transferBO = new TransferBO(
            accountRepository.findById(dto.getSourceAccountId()),
            accountRepository.findById(dto.getTargetAccountId())
        );
        transferBO.executeTransfer(dto.getAmount());  // 调用BO
        auditLog.logTransfer(dto);  // 协调审计日志
    }
}

‌案例3：医院预约系统‌

‌1. Domain层

// domain/entity/Appointment.java
public class Appointment {
    private Doctor doctor;
    private Patient patient;
    private LocalDateTime time;

    // 领域规则：校验预约时间有效性
    public boolean isValidTime() {
        return time.getHour() >= 9 && time.getHour() <= 17;
    }
}

2. BO层

// bo/AppointmentBO.java
public class AppointmentBO {
    private Appointment appointment;
    private ScheduleService scheduleService;

    // 业务逻辑：检查医生排班冲突
    public void checkConflict() {
        if (!scheduleService.isAvailable(appointment.getDoctor(), appointment.getTime())) {
            throw new ConflictException("医生该时段已排班");
        }
    }
}

‌3. Biz层

// biz/AppointmentService.java
public class AppointmentService {
    public void bookAppointment(AppointmentDTO dto) {
        AppointmentBO appointmentBO = new AppointmentBO(convertToEntity(dto));
        appointmentBO.checkConflict();  // 调用BO校验
        notificationService.sendConfirmation(appointmentBO.getAppointment());  // 协调通知
    }
}

‌关键总结‌

1. ‌Domain层‌：纯业务实体和规则，与技术无关
2. ‌BO层‌：组合多个领域对象的业务场景逻辑
3. ‌Biz层‌：协调领域逻辑与技术实现（如数据库、API调用）
4. ‌适用场景‌：复杂业务系统（如金融、电商、医疗），简单CRUD项目可合并BO和Biz层