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1. Introduction

In this quick tutorial, we're going to learn about the differences between @Component, @Repository, @Service annotations, in the Spring Framework.

Further reading:

Guide to Spring @Autowired

A guide to the most commonest usage of Springs @Autowired annotation and qualifiers

The Spring @Qualifier Annotation

@Autowired alone isn't sometimes enough to disambiguate dependencies. You can wire more exactly using the @Qualifier annotation. @Primary can also help.

2. Spring Annotations

In most typical applications, we have distinct layers like data access, presentation, service, business, etc.

And, in each layer, we have various beans. Simply put, to detect them automatically,  Spring uses classpath scanning annotations.

Then, it registers each bean in the ApplicationContext.

Here's a quick overview of a few of these annotations:

  • @Component is a generic stereotype for any Spring-managed component
  • @Service annotates classes at the service layer
  • @Repository annotates classes at the persistence layer, which will act as a database repository

We already have an extended article about these annotations. So we'll keep the focus only on the differences between them.

3. What's Different?

The major difference between these stereotypes is they are used for different classification. When we annotate a class for auto-detection, then we should use the respective stereotype.

Now, let's go through them in more detail.

3.1. @Component

We can use @Component across the application to mark the beans as Spring's managed components. Spring only pick up and registers beans with @Component  and doesn't look for @Service and @Repository in general.

They are registered in ApplicationContext because they themselves are annotated with @Component:

@Component
public @interface Service {
}
@Component
public @interface Repository {
}

@Service and @Repository are special cases of @Component. They are technically the same but we use them for the different purposes.

3.2. @Repository

@Repository’s job is to catch persistence specific exceptions and rethrow them as one of Spring’s unified unchecked exception.

For this Spring provides PersistenceExceptionTranslationPostProcessor, that requires to add in our application context:

<bean class=
  "org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>

This bean post processor adds an advisor to any bean that’s annotated with @Repository.

3.3. @Service

We mark beans with @Service to indicate that it's holding the business logic. So there's no any other specialty except using it in the service layer.

4. Conclusion

In this write-up, we learned about the differences between  @Component, @Repository, @Service annotations. We examined each annotation separately with the areas of their use.

As a conclusion, it's always a good idea to choose the annotation-based on their layer conventions.

 

Spring bottom

I just announced the new Learn Spring course, focused on the fundamentals of Spring 5 and Spring Boot 2:

>> CHECK OUT THE COURSE
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