Doc: Different behavior for @Named and @Component [SPR-14087]

[spring-projects-issues]

MD Sayem Ahmed opened SPR-14087 and commented

I am trying to understand the differences between these two annotations and how they affect injection in Spring. Consider the following piece of code -

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface ExternalPropertiesHolder {}

When I mark a class with this annotation -

@ExternalPropertiesHolder
public class SomeProperties {}

and then this dependency is injected using @Inject, it works perfectly -

@Service
public class SomeService {
    private SomeProperties someProperties;

    @Inject
    public SomeService(SomeProperties someProperties) {
        this.someProperties = someProperties;
    }
}

However, when I replace @Component with @Named -

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Named           // --> Here!
public @interface ExternalPropertiesHolder {}

Then the injection fails with the usual bean not found exception -

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.hogehoge.SomeProperties] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}

Shouldn't they behave the same way?

I am using Spring Boot 1.3.3.RELEASE version, and using JDK 8 to compile my application.

---

Reference URL: http://stackoverflow.com/questions/36203489/spring-differences-between-named-and-component

Backported to: 4.2.7

[spring-projects-issues]

Juergen Hoeller commented

I'm afraid those javax annotations are not designed for composability: Both javax.annotation.ManagedBean and javax.inject.Named can only be declared directly on a given bean class. The composable annotation story just works with Spring's own annotations.

[spring-projects-issues]

MD Sayem Ahmed commented

@Juergen Hoeller,

Thank you very much for answering!

[spring-projects-issues]

MD Sayem Ahmed commented

One suggestion though - can someone please update the documentation with a proper example? All I got from it is this -

JSR-330 does not provide a composable model, just a way to identify named components.

which I think is not enough for explanation.