meta annotation

#Meta annotation

If you have used CDI(introduced in Java EE 6), you could have been impressed by its stereotype feature. With a @Stereotype annotation, you can combine different concerns into one annotation and get both effectiveness when applied it in your classes.

In fact, in Spring world, this feature was existed for a long time, but it is not flexible as CDI.

Explore the codes of the @Controller, @Repository, and @Service, you can find they are all derived from the @Component annotation which is use for declaring a Spring managed bean.

But unfortunately, besides these annotations, you can not combine different annotations freely as CDI does. Thing has been changed when Spring 4 was born.

In Spring 4, you can combine different annotations into a new custom annotation freely.

For example, Spring 4 introduced a new annotation @RestController, which is just a combination of @Controller and @ResponseBody.

You can create your annotation like this, eg.

@Component
@Scope("request")
public interface @Model{

}

@Model annotation is a combination of @Component and @Scope, you can apply it on your new Java class, which indicates it is a request scoped component.

@Model
public class MyModel{

}

Another example, a @Repository class with @Transactional support.

@Repository
@Transactional
public class SignupRepository{

}

The @Repository and @Transactional can be extracted into a new annotation named @TransactionalRepository.

@Repository
@Transactional
public @interface TransactionalRepository{}

And apply the new @TransactionalRepository annotation on your repository class directly.

@TransactionalRepository
public class SignupRepository{

	@PersistenceContext 
	private EntityManager em;

	public Long save(Signup entity) {
		em.persist(entity);
		return entity.getId();
	}
	
	public Signup findById(Long id) {
		return em.find(Signup.class, id);
	}
}

Test code.

@Test
public void testSignup() {
	log.debug("call testSignup CURD@@@");

	Signup entity = new Signup("Hantsy", "Bai", "hantsy@gmail.com");

	Long savedId = signupRepository.save(entity);
	log.debug("saved id@" + savedId);
	assertTrue(savedId != null);
		
	Signup signup=signupRepository.findById(savedId);
	assertTrue(signup.getFirstName().equals("Hantsy"));
}

Check out the codes from my github.com, https://github.com/hantsy/spring4-sandbox.