我们如何利用自定义的@Qualifier 方法？

Question

I have multiple questions related to how annotation methods are implemented/utilized.

How can we utilize methods of a qualifier? Let's say I have a custom @Qualifier ie. @Store which represents an AppStore, and has 2 methods. How can I use the values passed to DeviceType deviceType() ?

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface Store {

    String value();

    DeviceType deviceType() default DeviceType.Phone;

    public enum DeviceType{
        Phone, Tablet;
    }

}

How does @Qualifier internally uses the String value() for matching the name? Is the same being overridden by the String value() when creating a custom @Qualifier ?

--- UPDATED INFO BELOW ---

I have a service that contains a field of type AppStore, which has an @Autowired and @Store annotation. How can i access the deviceType passes in the annotation after getting a bean of iPadAppStoreService?

@Service
public class iPadAppStoreService {

....

    @Autowired(required=false)
    @Store(value = "appleAppStore",
    deviceType = DeviceType.Tablet)
    private AppStore applicationStore;

....
}

Answer 1

How can we utilize methods of a qualifier?

You call them.

---

Let's say I have a custom @Qualifier ie. @Store which represents an AppStore, and has 2 methods. How can I use the values passed to DeviceType deviceType() ?

Store storeAnnotation = clazz.getAnnotation(Store.class);
DeviceType deviceType = storeAnnotation.deviceType();

where clazz is a class that has been annotated with @Store .

---

How does @Qualifier internally uses the String value() for matching the name?

If an @Autowired field/method/parameter finds multiple candidates by type and there is also a @Qualifier annotation (or a derived annotation like @Store ), it will look for a candidate type that has been annotated with @Qualifier with a matching value element.

---

Is the same being overridden by the String value() when creating a custom @Qualifier ?

Yes, the @Store annotation will be treated the same way as the @Qualifier annotation, ie its element values will be used the same way. Any extra element values are ignored by Spring, and will only be used by code you add.