Spring Container and Bean with configuration class(1)

✅ Spring Container and Bean

• ✔️ Spring container: manage object creation and DI and overall flow of the application
  • Spring container 🟰 ApplicationContext

• ✔️ Bean: Object that is added to Spring container

  • Java object that is managed by the Spring container
  • special object that Spring takes care for you - creates, manages dependencies, manage life cycle
• add annotation @Configuration

• Spring container will use @Configuration as DI information/metadata

• Spring container wil call all methods with @Bean and add it to spring container
• only creates the @Bean once

💡 How to add Bean

• @Bean등록하는 방법
• 1️⃣ manual bean configuration with @Configuration
• 2️⃣ component scan with @ComponentScan, @Autowired

• 이 게시글에서는 1️⃣번 방법에 대해 설명한다

• 1️⃣ Create Spring container @Configuration class
• Spring does not magically know what to add as bean ➡️ add what you want to add as bean in @Configuration class

@Configuration
public class AppConfig {
}

ApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);

//get memberService from AppCofig called by Spring container
MemberService memberService = applicationContext.getBean("memberService", MemberService.class);

• 2️⃣ Add beans to Spring container
• add @Bean as Spring bean to Spring container

@Configuration
public class AppConfig {

    @Bean
    public MemberService memberService(){
        return new MemberServiceImpl(memberRepository());
    }

✅ Get beans in test code

AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext(AppConfig.class);

//print all beans
String[] beanDefinitionNames = ac.getBeanDefinitionNames();

//find bean by name
MemberService memberService = ac.getBean("memberService", MemberService.class);

//find bean by type
//이 때 type아래 여러개 있으면 에러
MemberService memberService = ac.getBean(MemberService.class);

//type아래 있는 모든 bean 다 find
Map<String, MemberRepository> beansOfType = ac.getBeansOfType(MemberRepository.class);

• 부모 type으로 bean을 찾아오면 부모 ➕ 그 자식들도 모두 찾아온다
• bean not found: NoSuchBeanDefinitionException
• 하나의 클래스 안에 bean이 여러개: NoUniqueBeanDefinitionException

✅ Bean Factory

ApplicationContext implements ➡️ Bean Factory(interface)

• ✔️ Bean Factory: manage and find beans

  • getBean(), getBeansOfType() 메소드 등 모두 Bean Factory의 기능이다
• Spring container인 ApplicationContext은 Bean Factory를 상속받아
• Bean Factory의 기능들에 자신의 기능들을 추가해서 Spring container를 구현한다.