Dinesh on Java

+------------+-----------------------------------------------------+

| Annotation | Meaning                                             |
+------------+-----------------------------------------------------+
| @Component | generic stereotype for any Spring-managed component |
| @Repository| stereotype for persistence layer                    |
| @Service   | stereotype for service layer                        |
| @Controller| stereotype for presentation layer (spring-mvc)      |

+------------+-----------------------------------------------------+

@Component
public class Circle
{
    private Point center;
    ----
}

@Repository
public class CircleDaoImpl implements CircleDao
{
    private Point center;
    ----
}

Target:

@Service
public class CircleServiceImpl implements CircleService
{
    private Point center;
    ----
}

Target:

@Controller
public class CircleController
{
    private Point center;
    ----
}

Enable component scanning
Spring by default does not scan means Spring container does create bean for those classes whose annotated with above for stereotype annotations. So we have to enable component scanning explicity by using “context:component-scan” tag in your applicationContext.xml file. So stereotype annotations will be scanned and configured only when they are scanned by DI container of spring framework.

<context:component-scan base-package="com.dineshonjava.app.service" />
<context:component-scan base-package="com.dineshonjava.app.dao" />
<context:component-scan base-package="com.dineshonjava.app.controller" />

The context:component-scan element requires a base-package attribute, the value of base-package attribute should specifies a starting point for a recursive component search. Spring recommends do not use your top package for scanning, so you should declare specific component-scan elements.

Note: If you are using component-scan property for context namespace then you no longer need to declare context:annotation-config, because autowiring is implicitly enabled when component scanning is enabled.

Where to use stereotype annotations?
Always use these annotations over concrete classes; not over interfaces.

• @Controller annotation is for a class as a Spring Web MVC controller. It is a meta annotation of @Component, so beans annotated with it are automatically imported into the Spring container. If you add the @Controller annotation to a class then you can use handler mappling annotation i.e. @RequestMapping; to map URLs to instance methods of a class.
• @Service annotation is for a class as a Service of application.
• @Repository annotation is more suitable annotation that provides additional benefits specifically for DAOs. The @Repository annotation is a meta annotation 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 eligible for translation into Spring DataAccessException.
• @Component should be used when your class does not fall into either of three categories i.e. Controllers, Services and DAOs.