What's the difference between @Component, @Repository & @Service annotations in Spring?

java

annotations

spring

aop

byAnton Shumikhin·Aug 21, 2024

Within the Spring ecosystem, the annotations @Component, @Repository, and @Service serve as roles that you can associate with your beans:

@Component: For any Spring-managed class.
@Repository: An interface for Data Access Object (DAO) with persistence exception translation built-in for DB interactions.
@Service: Represents business logic, usually sits between repositories and controllers.

@Component
public class UnclassifiedBean {} // The humble underdog of components no one asked for

@Repository
public class CrudMasterRepository { /* Manages DB ops like a fast & furious DB driver */ }

@Service
public class BusinessGeniusService { /* Cooking up some serious logic here, heat's on! */ }

@Component, @Repository, and @Service not only categorize beans, but they also acquaint Spring with the purpose of the beans, making it easier for the framework to offer additional services such as exception handling for @Repository.

Annotations demystified: From an application perspective

Delineating application layers with annotations

@Component: When nothing fits in rest of the options, opt for me!

The Spring bean that sets the stage for specific roles to shine.
@Service: Flamboyant orchestrator of business rallies.

Dominates business logic, often between the frontline controller & the backend repository.
@Repository: The Gatekeeper of your database realm.

A specialist for Data Access Object (DAO) functions. Can soothe the deadly DB exceptions into a more palatable Spring DataAccessException.

Annotations catering to Aspect-Oriented Programming (AOP)

Spring's AOP can snugly fit into classes marked with @Service, @Controller, and @Repository, making it easier to implement aspects like transactions or logging with precision, upholding the maintainability and performance of your application.

Customization freedom with annotations

These annotations are composable. You can create your custom stereotype annotations, igniting @Component with your own flavors, for instance:

Need some code to run at regular intervals? Say hello to our little friend, @ScheduledJob.

Exception handling: A @Repository special

With @Repository, the DAO gets an upgrade by translating standard persistence exceptions into Spring's unchecked data access exceptions i.e., DataAccessException.

Practitioner's guide to using Spring stereotypes

Semantic clarity is the key

Choose @Repository for DB related operations considering its in-built exception translation, use @Service for implementing business logic. These annotations signal purpose, aiding code readability and layer distinction.

Watch out for some gotchas!

Don't overuse @Component. Let @Repository & @Service have their fair share of fun!
Did the <context:component-scan> miss the bus to your configuration? Add it, else your beans might remain invisible to Spring.

Structuring your application

Using the appropriate Stereotype annotations bolsters a well-structured application, each annotation attuned to its area of concern.

explain-codes / Java / What's the difference between @Component, @Repository & @Service annotations in Spring?

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