All four mark a class as a Spring bean that component scanning picks up. They are stereotype annotations, and @Service, @Repository and @Controller are specializations of @Component that also name the layer the class belongs to.
@Component is the generic stereotype for any Spring-managed class.
@Service marks business logic in the service layer.
@Repository marks data access. It also turns on exception translation, which converts database-specific exceptions into Spring's DataAccessException hierarchy.
@Controller marks the presentation layer. Spring MVC treats these classes as handlers for HTTP requests.
@Service
public class UserService { }
@Repository
public class UserRepository { }
@Controller
public class UserController { }
For component scanning, the four behave the same. The specific annotation still matters, because tools and aspects can target a layer by its annotation. Spring may also give these annotations more behavior in future versions, so use the one that matches the role of the class.
Rewriting in plainer words…
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