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Spring Boot : @Primary and @Qualifier

March 10, 2025
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Let's say we have a PaymentProcessorService in our application. This service needs to send notifications to users and for this, the class requires the NotificationManagementService type instance to be injected.


The NotificationManagementService has three implementations: SMSNotificationManagementService, PushNotificationManagementService, and EmailNotificationManagementService. Based on the use case, when we use PaymentProcessorService, we need to inject SMS, Push, and/or Email notification management services accordingly. 


But will the following code work?


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@Service
public class SMSNotificationManagementService implements NotificationManagementService {
}

@Service
public class PushNotificationManagementService implements NotificationManagementService {
}

@Service
public class EmailNotificationManagementService implements NotificationManagementService {
}



// INJECTING
@Service
public class PaymentProcessorService {

    private final NotificationManagementService notificationManagementService;

    @Autowired
    public PaymentProcessorService(NotificationManagementService notificationManagementService) {
        this.notificationManagementService = notificationManagementService;
    }
}


Answer is No


This will throw a NoUniqueBeanDefinitionException because Spring Boot finds multiple beans registered for NotificationManagementService and cannot decide which one to use.


So, it's obvious that we need a way to tell the application which bean to use and when. That's where the annotations @Primary and @Qualifier come in.


  • @Primary: Use this on the bean that should be injected by default.
  • @Qualifier("<bean_name>"): Use this to instruct the application to inject a specific bean other than the default. We need to provide the registered bean name as the @Qualifier parameter. (By default, Spring takes the class name, converts the first letter to lowercase and use it as bean name)

Now, let's look at the above code again, but this time using these annotations:


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@Service
public class SMSNotificationManagementService implements NotificationManagementService {
}

@Service
@Primary
public class PushNotificationManagementService implements NotificationManagementService {
}

@Service
public class EmailNotificationManagementService implements NotificationManagementService {
}



Injecting Beans with @Primary and @Qualifier


By default, PushNotificationManagementService will be injected because of @Primary


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@Autowired
public PaymentProcessorService(NotificationManagementService notificationManagementService) {
    this.notificationManagementService = notificationManagementService;
}


To inject SMSNotificationManagementService, we use @Qualifier


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@Autowired
public PaymentProcessorService(
    @Qualifier("sMSNotificationManagementService") NotificationManagementService notificationManagementService
) {
    this.notificationManagementService = notificationManagementService;
}


To inject EmailNotificationManagementService, we specify it with @Qualifier


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@Autowired
public PaymentProcessorService(
    @Qualifier("emailNotificationManagementService") NotificationManagementService notificationManagementService
) {
    this.notificationManagementService = notificationManagementService;
}


By this way we reduce ambiguidy and define which bean to be injected explicitly. Also if we used custom bean names, we have to use those names within Qualifier annotation to define the bean to be injected. 


Happy Coding 🙌


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