Difference between @Qualifier("beanName") and @Component("beanName")

Question

Is there any difference between using @Qualifier("beanName") and @Component("beanName") ? If not, is there a preferred approach?

Answer 1

Generally, you use @Component("beanName") on the component, You use @Qualifier("beanName") on a class you are autowiring. Ex

@Component("myComponent1")
public class MyComponent1 implements MyComponent {
....

}

@Component("myComponent2")
public class MyComponent2 implements MyComponent {
....

}

@Service
public class SomeService implements MyService {

    @Qualifier("myComponent1")
    private MyComponent myComponent;

    ...

}

If there is more than one implementation of a bean/component, spring won't know which bean to select, so you need to use a the qualifier to specify which one is correct.

Additionally, you can use @Primary on one of the components, so it is always selected by default.

Answer 2

They are totally two different things , sound like you are compare apple and orange to me.

@Component is used to declare a class as a Spring bean which you cannot do it with @Qualifier.

@Qualifier is intended to help Spring to determine which bean to inject if there are more than 1 eligible bean for that injection. It is normally used with @Autowired which add more constraint on the injection point such that there are only one bean can be injected in it.