What is difference between Component, Repository, Service, Controller & RestController

Upasana | August 12, 2019 | 2 min read | 731 views

Spring provide 4 basic stereotype annotations.

@Component

@Component is a generic stereotype for any Spring-managed component. Such classes are considered as candidates for auto-detection when using annotation-based configuration and classpath scanning.

Rest three annotations (@Repository, @Service, @Controller & @RestController) are meant for a specific purpose.

@Repository

The @Repository annotation is a marker for any class that fulfills the role oor stereotype of a repository (also known as DAO - Data Access Object). One of the main uses of this marker is the automatic translation of exceptions using an implementation of PersistenceExceptionTranslator. DAO throws a subclass of a HibernateException (if we are using Hibernate), which is a RuntimeException. Spring will automatically convert these Hibernate specific Runtime Exceptions to Spring specific exception.

<!-- Exception translation bean post processor -->
<bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>

The postprocessor automatically looks for all exception translators (implementations of the PersistenceExceptionTranslator interface) and advises all beans marked with the @Repository annotation so that the discovered translators can intercept and apply the appropriate translation on the thrown exceptions.

Spring Docs: Exception Translation

Some of the exception translations from HibernateExceptionTranslator are:

Exception Translation from Hibernate to Spring (HibernateExceptionTranslator)
Hibernate Exception	Spring Exception
NonUniqueObjectException	DuplicateKeyException
StaleObjectStateException	ObjectOptimisticLockingFailureException
TransientObjectException	InvalidDataAccessApiUsageException
ConstraintViolationException	DataIntegrityViolationException

@Service

It is a specialization of @Component Indicating that an annotated class is a "Service", originally defined by Domain-Driven Design (Evans, 2003) as "an operation offered as an interface that stands alone in the model, with no encapsulated state." May also indicate that a class is a "Business Service Facade" (in the Core J2EE patterns sense), or something similar.

@Controller

@Controller is a specialization of @Component hinting that the annotated class is a Web Controller.

@RestController

A convenience annotation that is itself annotated with @Controller and @ResponseBody.

Summary
@Component	generic stereotype for any Spring-managed component
@Repository	stereotype for persistence layer (DAO classes)
@Service	stereotype for service layer
@Controller	stereotype for presentation layer (spring-mvc)