Annotations

Annotations

Here are the annotations

1. @Required The @Required annotation applies to bean property setter methods and it indicates that the affected bean property must be populated in XML configuration file at configuration time. Otherwise, the container throws a BeanInitializationException exception. Required Annotation

2. @Autowired The @Autowired annotation provides more fine-grained control over where and how autowiring should be accomplished. The @Autowired annotation can be used to autowire bean on the setter method just like @Required annotation, constructor, a property or methods with arbitrary names and/or multiple arguments. Autowired Annotation

3. @Qualifier You can use the @Qualifier annotation along with @Autowired to remove the confusion by specifying which exact bean will be wired. Following is an example to show the use of @Qualifier annotation. Qualifier Annotation

Component Scanning

Spring can automatically scan a package for beans if component scanning is enabled.

@ComponentScan configures which packages to scan for classes with annotation configuration. We can specify the base package names directly with one of the basePackages or value arguments (value is an alias for basePackages):

@Configuration
@ComponentScan(basePackages = "com.baeldung.annotations")
class VehicleFactoryConfig {}

@Component

@Component is a class level annotation. During the component scan, Spring Framework automatically detects classes annotated with @Component. Since @Repository, @Service, @Configuration, and @Controller are all meta-annotations of @Component, they share the same bean naming behavior. Also, Spring automatically picks them up during the component scanning process.

@Repository

DAO or Repository classes usually represent the database access layer in an application, and should be annotated with @Repository: One advantage of using this annotation is that it has automatic persistence exception translation enabled. When using a persistence framework such as Hibernate, native exceptions thrown within classes annotated with @Repository will be automatically translated into subclasses of Spring’s DataAccessExeption. To enable exception translation, we need to declare our own **PersistenceExceptionTranslationPostProcessor **bean:

@Bean
public PersistenceExceptionTranslationPostProcessor exceptionTranslation() {
    return new PersistenceExceptionTranslationPostProcessor();
}

@Service

The business logic of an application usually resides within the service layer – so we’ll use the @Service annotation to indicate that a class belongs to that layer:

@Controller

@Controller is a class level annotation which tells the Spring Framework that this class serves as a controller in Spring MVC: