Java优学网Spring依赖注入讲解：告别手动管理，轻松实现对象解耦与高效开发

// 传统方式 - 对象自己管理依赖 public class UserService {

private UserRepository userRepository = new UserRepository();

}

@Service public class OrderService {

private final PaymentProcessor paymentProcessor;
private final InventoryService inventoryService;

@Autowired
public OrderService(PaymentProcessor paymentProcessor, 
                   InventoryService inventoryService) {
    this.paymentProcessor = paymentProcessor;
    this.inventoryService = inventoryService;
}

}

@Service public class UserService {

private final UserRepository userRepository;
private NotificationService notificationService;

@Autowired
public UserService(UserRepository userRepository) {
    this.userRepository = userRepository;
}

@Autowired
public void setNotificationService(NotificationService notificationService) {
    this.notificationService = notificationService;
}

}

@Component public class ServiceA {

private final ServiceB serviceB;

public ServiceA(ServiceB serviceB) {
    this.serviceB = serviceB;  // 等待ServiceB创建
}

}

@Component
public class ServiceB {

private final ServiceA serviceA;

public ServiceB(ServiceA serviceA) {
    this.serviceA = serviceA;  // 等待ServiceA创建
}

}