关于@Qualifier("beanName")用法

import org.springframework.stereotype.Service;

@Service("emailNotifier") // 给这个Bean起一个限定名 "emailNotifier"
public class EmailNotificationService implements NotificationService {
    // ...
}

import org.springframework.stereotype.Service;

@Service("smsNotifier") // 给这个Bean起一个限定名 "smsNotifier"
public class SmsNotificationService implements NotificationService {
    // ...
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

@Service
public class OrderService {
    private final NotificationService notificationService;

    @Autowired
    public OrderService(@Qualifier("emailNotifier") NotificationService notificationService) {
        // @Qualifier说：在所有NotificationService类型的Bean中，
        // 我就要那个名字叫 "emailNotifier" 的！
        this.notificationService = notificationService;
    }
    // ...
}

@Service
public class UrgentOrderService {
    private final NotificationService notificationService;

    @Autowired
    public UrgentOrderService(@Qualifier("smsNotifier") NotificationService notificationService) {
        // 这里明确指定了需要短信通知服务
        this.notificationService = notificationService;
    }
    // ...
}

@Service("emailNotifier")
@Primary // Email服务是首选
public class EmailNotificationService implements NotificationService { ... }

@Service("smsNotifier")
public class SmsNotificationService implements NotificationService { ... }

// --- 消费者 ---
@Service
public class OrderService {
    private final NotificationService notificationService;

    @Autowired
    public OrderService(@Qualifier("smsNotifier") NotificationService notificationService) {
        // 尽管Email是@Primary，但这里通过@Qualifier明确指定了smsNotifier
        this.notificationService = notificationService;
    }

    public void placeOrder() {
        // 这将调用 SmsNotificationService
        notificationService.sendNotification("您的订单已成功创建！");
    }
}