Bean LifeCycle

0. 들어가면서

Bean LifeCycle

• 해당 객체가 생성되고 소멸될까지의 과정을 나타냄(when, how)
• Spring은 3가지 방법으로 Bean LifeCycle Callback을 관리

---

1. Bean LifeCycle Flow

1. Create Spring Container
2. Create Spring Bean
3. Dependencies Injected
4. Bean Initialize : After 2,3 step
5. Use
6. Callback Before Destroy : Before Bean Destroyed
7. Spring Off

---

2. Callback

• Spring Framework는 Bean LifeCycle 제어를 위해 다음과 같은 방법을 제공

1. Interfaces( InitializingBean & DisposableBean )
2. Setting Method( initialize() & close() )
3. Annotation( @PostConstruct & @PreDestroy )

2.1 InitializingBean & DisposableBean

• InitializingBean : Bean에 필요한 속성들이 Container에 설정된 후 Bean Initialize Callback

• DisposableBean : Spring Container가 Bean을 소멸하기 전 Bean Destroy Callback

public class Example implements InitializingBean, DisposableBean {
    public Example()  {
        System.out.println("Constructor Callback");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("Initialization");
        //Bean Initialization Code
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("Destruction");
        //Bean Destruction Code
    }
}

• Interface를 이용한 Initialize, Destroy 방법(Spring 초창기에 사용하던 방법)

2.2 initialize() & destroy()

• @Bean에 initMethod, destroyMethod 속성을 이용하여 Initialize, Destroy

• @Bean(initMethod = “initialize”, destroyMethod = “close”)

public class Example{

    public void initialize() throws Exception{
        System.out.println("Initialization");
        //Bean Initialization Code
    }
    public void close() throws Exception{
        System.out.println("Destruction");
        //Bean Destruction Code
    }
}

@Configuration
class LifeCycleConfigi{
    @Bean(initMethod = "initialize", destroyMethod = "close")
    public Example example(){
    
    }
}

2.3 @PostConstruct & @PreDestroy

• @PostConstruct : Bean이 생성 후 Instance가 요청 객체에 반환되기 직전에 Callback

• @PreDestroy : Bean Container 내부에서 Bean Destroy 직전에 Callback

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

public class Example{
	@PostConstruct
	public void customInit(){
		System.out.println("Customized Initialize Method Callback");
	}

	@PreDestroy
	public void customDestroy(){
		System.out.println("Customized Destroy Method Callback");
	}
}

• Annotation을 통해서 Callback 함수들을 Cuustomize(최신 스프링에서 권장하는 방식)

---

3. Comparation

	Interface	Config Method	Annotation
Usage In External Library	X	O	X
Spring Code Dependency	O	X	X

• 코드 수정이 불가능한 외부 라이브러리에는 설정 정보에 초기화, 종료 메소드 지정 방식 방식을 사용하는 것이 좋음
• initialize() & destroy()

---