구르는 돌에는 이끼가 끼지 않는다

회사 코드에 EntityManager를 사용하여 try~catch~finally를 사용하여 finally에서 해당 EntityManager 인스턴스를 close()하고 자원을 반납하고 있었습니다. 

하지만 이펙티브 자바에서는 [아이템 9. try-finally 대신 try-with-resources를 사용하라.] 라는 내용이 존재합니다. 

그래서 EntityManager를 try-with-resources로 리팩터링을 하려고 했지만, AutoClosable이 지원하지 않는다고 IDE에서 말해주고 있었습니다. 관련 글을 찾던 중 블로그에 해당 이슈는 오픈소스에 fix issue로 등록이 되어 있고 특정 버전 이후에 추가가 되었다고 합니다.

제가 회사에서 쓰는 java persistence-api 라이브러리는 2.x로 AutoClosable을 지원하지 않았고, 3.x대로 올라가면서 Jakarta Persistence API -> 3.1.0 지원하게 된것을 알게되었습니다.

EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("default");
try(EntityManager entityManager = entityManagerFactory.createEntityManager()){

}

package jakarta.persistence;

import jakarta.persistence.criteria.CriteriaBuilder;
import jakarta.persistence.criteria.CriteriaDelete;
import jakarta.persistence.criteria.CriteriaQuery;
import jakarta.persistence.criteria.CriteriaUpdate;
import jakarta.persistence.metamodel.Metamodel;
import java.util.List;
import java.util.Map;

public interface EntityManager extends AutoCloseable {
    void persist(Object var1);

    <T> T merge(T var1);

    void remove(Object var1);

해당 Jakarta Persistence API의 EntityManager 인터페이스를 보면 알 수 있듯이 해당 클래스는 AutoCloseable을 상속하고 있는 것을 알 수 있습니다.

public interface AutoCloseable {
    /**
     * Closes this resource, relinquishing any underlying resources.
     * This method is invoked automatically on objects managed by the
     * {@code try}-with-resources statement.
     *
     * <p>While this interface method is declared to throw {@code
     * Exception}, implementers are <em>strongly</em> encouraged to
     * declare concrete implementations of the {@code close} method to
     * throw more specific exceptions, or to throw no exception at all
     * if the close operation cannot fail.
     *
     * <p> Cases where the close operation may fail require careful
     * attention by implementers. It is strongly advised to relinquish
     * the underlying resources and to internally <em>mark</em> the
     * resource as closed, prior to throwing the exception. The {@code
     * close} method is unlikely to be invoked more than once and so
     * this ensures that the resources are released in a timely manner.
     * Furthermore it reduces problems that could arise when the resource
     * wraps, or is wrapped, by another resource.
     *
     * <p><em>Implementers of this interface are also strongly advised
     * to not have the {@code close} method throw {@link
     * InterruptedException}.</em>
     *
     * This exception interacts with a thread's interrupted status,
     * and runtime misbehavior is likely to occur if an {@code
     * InterruptedException} is {@linkplain Throwable#addSuppressed
     * suppressed}.
     *
     * More generally, if it would cause problems for an
     * exception to be suppressed, the {@code AutoCloseable.close}
     * method should not throw it.
     *
     * <p>Note that unlike the {@link java.io.Closeable#close close}
     * method of {@link java.io.Closeable}, this {@code close} method
     * is <em>not</em> required to be idempotent.  In other words,
     * calling this {@code close} method more than once may have some
     * visible side effect, unlike {@code Closeable.close} which is
     * required to have no effect if called more than once.
     *
     * However, implementers of this interface are strongly encouraged
     * to make their {@code close} methods idempotent.
     *
     * @throws Exception if this resource cannot be closed
     */
    void close() throws Exception;
}

https://k3068.tistory.com/98

https://www.inflearn.com/questions/231224/entitymanager-%EB%8A%94-%EC%99%9C-autocloseable-%EC%9D%84-%EC%A7%80%EC%9B%90%ED%95%98%EC%A7%80-%EC%95%8A%EB%82%98%EC%9A%94