in spring

Spring MVC @component, @controller, @Repository and @service annotations

Spring @Component, @Service, @Repository, and @Controller annotations are used for automatic bean detection using classpath scan in Spring framework. @Component is a generic annotation. Difference of @Service, @Repository, @Controller with @Component is they are special cases of @Component and used for particular purposes.

@Component Annotation

The @Component annotation marks a java class as a bean so the component-scanning mechanism of spring can pick it up and pull it into the application context. To use this annotation, apply it over class as below:

@Component
public EmployeeDAOImpl implements EmployeeDAO 
{    
   ...
}

@Controller Annotation

@Controller annotation marks a class as a Spring Web MVC controller. It too is a @Componentspecialization, so beans marked with it are automatically imported into the DI container. When we add the @Controller annotation to a class, we can use another annotation i.e. @RequestMapping; to map URLs to instance methods of a class.

@Service Annotation

The @Service annotation is also a specialization of the component annotation. It doesn’t currently provide any additional behavior over the @Component annotation, but it’s a good idea to use @Service over @Component in service-layer classes because it specifies intent better. Additionally, tool support and additional behavior might rely on it in the future.

@Repository Annotation

Although above use of @Component is good enough but we can use more suitable annotation that provides additional benefits specifically for DAOs i.e. @Repository annotation. The @Repository annotation is a specialization of the @Component annotation with similar use and functionality. In addition to importing the DAOs into the DI container, it also makes the unchecked exceptions (thrown from DAO methods) eligible for translation into Spring DataAccessException.