Component scanning and stereotypes

Definition

Component scanning makes Spring search a package for classes marked @Component and register them as beans. @Service, @Repository and @Controller are the same thing with a clearer meaning, and @Repository also translates database exceptions.

Example code

Finding beans by scanning

import java.util.Arrays;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;

@Component class Clock2 { }
@Service class BillingService { }
@Repository class CustomerRepository { }
class NotABean { }                                              // no stereotype: Spring ignores it

@ComponentScan                                                  // scans this class's package
class Demo {
    public static void main(String[] args) {
        try (var context = new AnnotationConfigApplicationContext(Demo.class)) {
            String[] names = context.getBeanDefinitionNames();
            Arrays.stream(names).filter(n -> !n.contains(".") && !n.equals("demo")).sorted().forEach(System.out::println);
        }
    }
}

// Output:
// billingService
// clock2
// customerRepository