JPA

build.gradle

	implementation 'org.springframework.boot:spring-boot-starter-data-jpa'

application.properties

spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=none

JpaMemberRepository.java

package hello.hellospring.repository;

import hello.hellospring.domain.Member;
import org.hibernate.annotations.common.reflection.XMember;

import javax.persistence.EntityManager;
import java.util.List;
import java.util.Optional;

public class JpaMemberRepository implements MemberRepository {

    private final EntityManager em;

    public JpaMemberRepository(EntityManager em) {
        this.em = em;
    }

    @Override
    public Member save(Member member) {
        em.persist(member);
        return member;
    }

    @Override
    public Optional<Member> findById(Long id) {
        Member member = em.find(Member.class, id);
        return Optional.ofNullable(member);
    }

    @Override
    public Optional<Member> findByName(String name) {
        List<Member> result = em.createQuery("select m from Member m where m.name = :name", Member.class)
                .setParameter("name", name)
                .getResultList();

        return result.stream().findAny();
    }

    @Override
    public List<Member> findAll() {
        return em.createQuery("select m from Member m", Member.class)
                .getResultList();
    }
}

Member.java

 @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

MemberService.java

@Transactional
public class MemberService {

스프링데이터 JPA

SpringDataMemberRepository.java

package hello.hellospring.repository;


import hello.hellospring.domain.Member;
import org.springframework.data.jpa.repository.JpaRepository;

import java.util.Optional;

public interface SpringDataJpaMemberRepository extends JpaRepository<Member, Long>, MemberRepository {
    @Override
    Optional<Member> findByName(String name);
}

Spring.Config

@Configuration
public class SpringConfig {

    private final MemberRepository memberRepository;

    @Autowired
    public SpringConfig(MemberRepository memberRepository) {
        this.memberRepository = memberRepository;
    }

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

//    @Bean
//    public MemberRepository memberRepository(){
        //return new MemoryMemberRepository();
        //return new JdbcMemberRepository(dataSource);
        //return new JdbcTemplateMemberRepository(dataSource);
        //return new JpaMemberRepository(em);
//    }
}

AOP

AOP가 필요한 상황

• 모든 메소드의 호출 시간을 측정하고 싶다면?
• 공통관심사항(cross-cutting concern) 핵심 관심 사항(core concern)

long start = System.currentTimeMillis();

        try{
            //중복 회원 검증
            validateDuplicateMember(member);
            memberRepository.save(member);
            return member.getId();
        }finally{
            long finish = System.currentTimeMillis();
            long timeMs = finish - start;
            System.out.println("join = " + timeMs + "ms");
        }

문제

• 시간을 측정하는 로직은 공통 관심 사항이다.
• 시간을 측정하는 로직을 변경할때 모든 로직을 찾아가면서 변경해야 한다.

AOP 적용

• AOP: Aspect Oriented Programming
• 공통 관심사항 vs 핵심 관심 사항 분리

package hello.hellospring.aop;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.stereotype.Component;

@Aspect
@Component
public class TimeTraceAop {

    @Around("execution(* hello.hellospring..*(..))")
    public Object execute(ProceedingJoinPoint joinPoint) throws Throwable {
        long start = System.currentTimeMillis();
        System.out.println("START: " + joinPoint.toString());
        try{
            return joinPoint.proceed();     //Ctrl alt shift T => inline
        } finally {
            long finish = System.currentTimeMillis();
            long timeMs = finish - start;
            System.out.println("END: " + joinPoint.toString() + " " + timeMs + "ms");
        }
    }
}

START: execution(String hello.hellospring.controller.MemberController.list(Model))
START: execution(List hello.hellospring.service.MemberService.findMembers())
START: execution(List org.springframework.data.jpa.repository.JpaRepository.findAll())
Hibernate: select member0_.id as id1_0_, member0_.name as name2_0_ from member member0_
END: execution(List org.springframework.data.jpa.repository.JpaRepository.findAll()) 144ms
END: execution(List hello.hellospring.service.MemberService.findMembers()) 149ms
END: execution(String hello.hellospring.controller.MemberController.list(Model)) 159ms

해결

• 시간을 측정하는 로직을 별도의 공통 로직으로 만들었다.
• 핵심 관심 사항을 깔끔하게 유지할 수 있다.
• 변경이 필요하면 이 로직만 변경하면 된다.
• 원하는 적용 대상을 선택할 수 있다.

스프링의 모든 것을 알수 없고 알 필요도 없다.

스프링 만드는 개발자가 아니니 스프링을 활용해서 실무에서 발생하는 문제들을 잘 해결하는 것이 중요하다.