Bean 생명주기와 콜백

스프링 빈은 객체생성 -> 의존관계주입의 라이프사이클을 가진다. (생성자 주입의 경우 예외)

스프링 빈은 객체를 생성하고, 의존관계 주입이 다 끝난 후에 필요한 데이터를 사용할 수 있는 준비가 완료된다. 따라서 의존관계 주입이 모두 완료되고 난 후에 초기화가 호출되야한다.

  • 스프링은 의존관계 주입이 완료되면 스프링 빈에 콜백 메서드를 통해서 초기화 시점을 알려주는 다양한 기능을 제공한다.

  • 스프링 컨테이너가 종료되기 직전에 소멸 콜백을 준다.

스프링 빈 이벤트 라이프사이클

  1. 스프링 컨테이너 생성

  2. 스프링 빈 생성

  3. 의존관계 주입

  4. 초기화 콜백 : 빈이 생성되고, 빈의 의존관계 주입이 완료된 후

  5. 사용

  6. 소멸전 콜백 : 빈이 소멸되기 직전에 호출

  7. 스프링 종료

생성자는 필수 정보를 받고, 메모리를 할당해서 객체를 생성하는 책임을 가진다.

초기화는 이렇게 생성된 값을 활용해서 외부 커넥션을 연결하는 등 무거운 동작을 수행한다.

즉, 생성자 안에서 초기화 작업을 함께 하는 것 보다는 객체를 생성하는 부분과 초기화 하는 부분은 명확하게 나누는 것이 유지보수 관점에 좋다.

콜백 방법

인터페이스 방법

InitializingBean, DisposableBean 을 구현하여, 초기화 메서드와 소멸 메서드를 설정할 수 있다.

  • InitializingBean

    public interface InitializingBean {

    /**
     * Invoked by the containing {@code BeanFactory} after it has set all bean properties
     * and satisfied {@link BeanFactoryAware}, {@code ApplicationContextAware} etc.
     * <p>This method allows the bean instance to perform validation of its overall
     * configuration and final initialization when all bean properties have been set.
     * @throws Exception in the event of misconfiguration (such as failure to set an
     * essential property) or if initialization fails for any other reason
     */
    void afterPropertiesSet() throws Exception;

}

  • DisposableBean

    public interface DisposableBean {

    /**
     * Invoked by the containing {@code BeanFactory} on destruction of a bean.
     * @throws Exception in case of shutdown errors. Exceptions will get logged
     * but not rethrown to allow other beans to release their resources as well.
     */
    void destroy() throws Exception;

}

  • 예제 클래스

    package dh0023.springcore.lifecycle;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;

/**
 * 테스트를 위한 가짜 NetworkClient
 */
public class NetworkClient implements InitializingBean, DisposableBean {

    private String url;

    public NetworkClient() {
        System.out.println("생성자 호출, url = " + url);
    }

    public void setUrl(String url) {
        this.url = url;
    }

    // start service
    public void connect() {
        System.out.println("connect: " + url);
    }

    public void call(String message) {
        System.out.println("call: " + url + " message = " + message);
    }

    public void disconnect() {
        System.out.println("close: " + url);
    }

    /**
     * 의존관계 주입 후 호출
     * @throws Exception
     */
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("NetworkClient.afterPropertiesSet");
        connect();
        call("초기화 연결 메세지");
    }

    /**
     * 소멸직후 콜백
     * @throws Exception
     */
    @Override
    public void destroy() throws Exception {
        System.out.println("NetworkClient.destroy");
        disconnect();
    }
}

  • Test Code

    ```java package dh0023.springcore.lifecycle;

    import org.junit.jupiter.api.Test; import org.springframework.context.ConfigurableApplicationContext; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Description;

    public class BeanLifeCycleTest {

    @Test
@Description("인터페이스 적용 테스트")
void lifeCycleInterfaceTest() {
    ConfigurableApplicationContext ac = new AnnotationConfigApplicationContext(LifeCycleConfig.class);
    NetworkClient client = ac.getBean(NetworkClient.class);
    ac.close();
}
  @Configuration
  static class LifeCycleConfig {
      @Bean
      public NetworkClient networkClient() {
          NetworkClient networkClient = new NetworkClient();
          networkClient.setUrl("http://spring-core.dev");
          return networkClient;
      }
  }

}

- 결과

23:23:39.553 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'networkClient' 생성자 호출, url = null NetworkClient.afterPropertiesSet connect: http://spring-core.dev call: http://spring-core.dev message = 초기화 연결 메세지 23:23:39.645 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@932bc4a, started on Sun May 16 23:23:38 KST 2021 NetworkClient.destroy close: http://spring-core.dev

Process finished with exit code 0

  1. Creating shared instance of singleton bean 'networkClient'
  2. 생성자 호출
  3. NetworkClient.afterPropertiesSet
  4. Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@932bc4a
  5. NetworkClient.destroy
  6. 스프링 종료

  다음과 같은 순서로 사이클이 수행되는 것을 확인할 수 있다.

#### 단점

- 스프링 전용 인터페이스이다. 해당 코드가 스프링 전용 인터페이스에 의존하게 된다.
- 초기화, 소멸 메서드의 이름을 변경할 수 없다.
- 외부 라이브러리에 적용할 수 없다.

이 방법은 초창기 나온 방법으로, 현재는 거의 사용하지 않는다.



### 설정 정보 사용(메서드 등록)

`@Bean` 어노테이션에 등록 초기화, 소멸 메서드를 설정하는 방법이다.

- 예제 클래스

  ```java
  /**
   * 테스트를 위한 가짜 NetworkClient
   */
  public class NetworkClientMethod {

      private String url;

      public NetworkClientMethod() {
          System.out.println("생성자 호출, url = " + url);

      }

      public void setUrl(String url) {
          this.url = url;
      }

      // start service
      public void connect() {
          System.out.println("connect: " + url);
      }

      public void call(String message) {
          System.out.println("call: " + url + " message = " + message);
      }

      public void disconnect() {
          System.out.println("close: " + url);
      }

      public void init() {
          System.out.println("NetworkClientMethod.init");
          connect();
          call("초기화 연결 메세지");

      }

      public void close() {
          System.out.println("NetworkClientMethod.close");
          disconnect();
      }

  }

  • 테스트 코드

    ```java package dh0023.springcore.lifecycle;

    import org.junit.jupiter.api.Test; import org.springframework.context.ConfigurableApplicationContext; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Description;

    public class BeanLifeCycleTest {

    @Test
@Description("메서드 적용 테스트")
void lifeCycleMethodTest() {
    ConfigurableApplicationContext ac = new AnnotationConfigApplicationContext(LifeCycleConfig.class);
    NetworkClientMethod client = ac.getBean(NetworkClientMethod.class);
    ac.close();
}
  @Configuration
  static class LifeCycleConfig {

      @Bean(initMethod = "init", destroyMethod = "close")
      public NetworkClientMethod networkClientMethod() {
          NetworkClientMethod networkClientMethod = new NetworkClientMethod();
          networkClientMethod.setUrl("http://spring-core.dev");
          return networkClientMethod;
      }
  }

}

- 결과

  ```java
  23:35:00.964 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'networkClientMethod'
  생성자 호출, url = null
  NetworkClientMethod.init
  connect: http://spring-core.dev
  call: http://spring-core.dev message = 초기화 연결 메세지
  23:35:01.128 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@932bc4a, started on Sun May 16 23:35:00 KST 2021
  NetworkClientMethod.close
  close: http://spring-core.dev

  Process finished with exit code 0

  1. Creating shared instance of singleton bean 'networkClientMethod'

  2. 생성자 호출

  3. 초기화 콜백 : NetworkClientMethod.init

  4. Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@932bc4a

  5. 소멸직후 콜백 : NetworkClientMethod.close

  6. 스프링 종료

특징

  • 메서드 이름을 자유롭게 줄 수 있다.

  • 스프링 빈이 스프링 코드에 의존하지 않는다.

  • 설정 정보를 사용하기 때문에 코드를 고칠 수 없는 외부 라이브러리에도 초기화, 종료 메서드를 적용할 수 있다.

@Bean destroyMethod

라이브러리 대부분 close, shutdown 과 같은 이름의 종료 메서드를 사용한다.

    String destroyMethod() default AbstractBeanDefinition.INFER_METHOD;
public static final String INFER_METHOD = "(inferred)";

destoryMethod() 의 default값은 (inferred) 로 등록되어 있다. 이 추론 기능은 close, shutdown 과 같은 이름의 메서드를 자동으로 호출해준다. 이름 그대로 종료 메서드를 추론해서 호출해주는 것이다.

따라서 직접 스프링 빈으로 등록하면 종료 메서드는 따로 적어주지 않아도 된다. 만약 추론기능을 사용하기 싫은 경우에는 destroyMethod="" 로 설정해주면 된다.

어노테이션 방법

  • @PostConstruct

    package javax.annotation;

import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;

/**
 * The <code>PostConstruct</code> annotation is used on a method that 
 * needs to be executed after dependency injection is done to perform 
 * any initialization. This  method must be invoked before the class 
 * is put into service. This annotation must be supported on all classes 
 * that support dependency injection. The method annotated with 
 * <code>PostConstruct</code> must be invoked even if the class does 
 * not request any resources to be injected. Only one 
 * method in a given class can be annotated with this annotation. 
 * The method on which the <code>PostConstruct</code> annotation is 
 * applied must fulfill all of the following criteria:
 * <ul>
 * <li>The method must not have any parameters except in the case of 
 * interceptors in which case it takes an <code>InvocationContext</code>
 * object as defined by the Interceptors specification.</li>
 * <li>The method defined on an interceptor class or superclass of an
 * interceptor class must have one of the following signatures:
 * <p>
 * void &#060;METHOD&#062;(InvocationContext)
 * <p>
 * Object &#060;METHOD&#062;(InvocationContext) throws Exception
 * <p>
 * <i>Note: A PostConstruct interceptor method must not throw application 
 * exceptions, but it may be declared to throw checked exceptions including 
 * the java.lang.Exception if the same interceptor method interposes on 
 * business or timeout methods in addition to lifecycle events. If a 
 * PostConstruct interceptor method returns a value, it is ignored by 
 * the container.</i>
 * </li>
 * <li>The method defined on a non-interceptor class must have the 
 * following signature:
 * <p>
 * void &#060;METHOD&#062;()
 * </li>
 * <li>The method on which the <code>PostConstruct</code> annotation
 * is applied may be public, protected, package private or private.</li>
 * <li>The method must not be static except for the application client.</li>
 * <li>The method should not be final.</li>
 * <li>If the method throws an unchecked exception the class must not be put into   
 * service except in the case where the exception is handled by an
 * interceptor.</li></ul>
 *
 * @see javax.annotation.PreDestroy
 * @see javax.annotation.Resource
 * @since 1.6, Common Annotations 1.0
 */
@Documented
@Retention (RUNTIME)
@Target(METHOD)
public @interface PostConstruct {
}

  • @PreDestroy

    package javax.annotation;

import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;

/**
 * The <code>PreDestroy</code> annotation is used on a method as a
 * callback notification to signal that the instance is in the
 * process of being removed by the container. The method annotated
 * with <code>PreDestroy</code> is typically used to
 * release resources that it has been holding. This annotation must be
 * supported by all container-managed objects that support the use of
 * the <code>PostConstruct</code> annotation except the Jakarta EE application 
 * client. The method on which the <code>PreDestroy</code> annotation
 * is applied must fulfill all of the following criteria:
 * <ul>
 * <li>The method must not have any parameters except in the case of
 * interceptors in which case it takes an <code>InvocationContext</code>
 * object as defined by the Interceptors specification.</li>
 * <li>The method defined on an interceptor class or superclass of an
 * interceptor class must have one of the following signatures:
 * <p>
 * void &#060;METHOD&#062;(InvocationContext)
 * <p>
 * Object &#060;METHOD&#062;(InvocationContext) throws Exception
 * <p>
 * <i>Note: A PreDestroy interceptor method must not throw application
 * exceptions, but it may be declared to throw checked exceptions including
 * the java.lang.Exception if the same interceptor method interposes on
 * business or timeout methods in addition to lifecycle events. If a
 * PreDestroy interceptor method returns a value, it is ignored by
 * the container.</i>
 * </li>
 * <li>The method defined on a non-interceptor class must have the
 * following signature:
 * <p>
 * void &#060;METHOD&#062;()
 * </li>
 * <li>The method on which PreDestroy is applied may be public, protected,
 * package private or private.</li>
 * <li>The method must not be static.</li>
 * <li>The method should not be final.</li>
 * <li>If the method throws an unchecked exception it is ignored by
 * the container.</li>
 * </ul>
 *
 * @see javax.annotation.PostConstruct
 * @see javax.annotation.Resource
 * @since 1.6, Common Annotations 1.0
 */

@Documented
@Retention (RUNTIME)
@Target(METHOD)
public @interface PreDestroy {
}

  • 테스트 클래스

    package dh0023.springcore.lifecycle;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;

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

/**
 * 테스트를 위한 가짜 NetworkClient
 */
public class NetworkClient {

    private String url;

    public NetworkClient() {
        System.out.println("생성자 호출, url = " + url);
    }

    public void setUrl(String url) {
        this.url = url;
    }

    // start service
    public void connect() {
        System.out.println("connect: " + url);
    }

    public void call(String message) {
        System.out.println("call: " + url + " message = " + message);
    }

    public void disconnect() {
        System.out.println("close: " + url);
    }

    /**
     * 의존관계 주입 후 호출
     * @throws Exception
     */
    @PostConstruct
    public void init() throws Exception {
        System.out.println("NetworkClient.init");
        connect();
        call("초기화 연결 메세지");
    }

    /**
     * 소멸직전 콜백
     * @throws Exception
     */
    @PreDestroy
    public void close() throws Exception {
        System.out.println("NetworkClient.close");
        disconnect();
    }
}

  • 테스트 코드

    ```java package dh0023.springcore.lifecycle;

    import org.junit.jupiter.api.Test; import org.springframework.context.ConfigurableApplicationContext; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Description;

    public class BeanLifeCycleTest { @Test @Description("어노테이션 방 적용 테스트") void lifeCycleTest() { ConfigurableApplicationContext ac = new AnnotationConfigApplicationContext(LifeCycleConfig.class); NetworkClient client = ac.getBean(NetworkClient.class); ac.close(); }

  @Configuration
  static class LifeCycleConfig {
      @Bean
      public NetworkClient networkClient() {
          NetworkClient networkClient = new NetworkClient();
          networkClient.setUrl("http://spring-core.dev");
          return networkClient;
      }
  }

}

- 결과

  ```java
  23:50:43.425 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'networkClient'
  생성자 호출, url = null
  NetworkClient.init
  connect: http://spring-core.dev
  call: http://spring-core.dev message = 초기화 연결 메세지
  23:50:43.557 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@932bc4a, started on Sun May 16 23:50:42 KST 2021
  NetworkClient.destroy
  close: http://spring-core.dev

특징

  • 최신 스프링에서 가장 권장하는 방법

  • 애노테이션만 붙이면 되므로 매우 편리

  • javax.annotation 패키지는 스프링 종속적인 기술이 아니라 자바 표준이다. 따라서, 스프링이 아닌 다른 컨테이너에서도 동작한다.

단점

  • 외부 라이브러리에 적용하지 못한다. 외부 라이브러리를 초기화/종료 해야하면 @Bean 의 기능을 사용해야한다.

참고

PreviousLombok 활용하기NextBean Scope

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