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1. Introduction

In this quick tutorial, we're going to learn about the differences between the @Component, @Repository, and @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.

Additionally, in each layer we have various beans. To detect these beans 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 here to the differences between them.

3. What's Different?

The major difference between these stereotypes is that they are used for different classifications. When we annotate a class for auto-detection, 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 will only pick up and register beans with @Component, and doesn't look for @Service and @Repository in general.

They are registered in ApplicationContext because they 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 re-throw them as one of Spring’s unified unchecked exceptions.

For this, Spring provides PersistenceExceptionTranslationPostProcessor, which we are required to add in our application context (already included if we're using Spring Boot):

<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 they're holding the business logic. Besides being used in the service layer, there isn't any other special use for this annotation.

4. Conclusion

In this article, we learned about the differences between the @Component, @Repository, and @Service annotations. We examined each annotation separately to understand their areas of use.

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

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