재학습_7일차 스프링 DB 접근 기술_1

# 스프링 DB 접근 기술

## H2 데이터베이스 설치

• H2 데이터베이스 : 개발, 테스트 용도로 가볍고 편리한 DB, 웹 화면 제공.
• https://www.h2database.com/html/download-archive.html

Archive Downloads

테이블 생성
drop table if exists member CASCADE;
create table member
(
    id bigint generated by default as identity,
    name varchar(255),
    primary key (id)
);


조회
select * from member;


추가
insert into member(name) values('베리');

## 순수 JDBC (고전 스타일)

• 아래와 같이 JDBC 환경설정 진행.
• build.gradle 파일에 jdbc, h2 데이터베이스 관련 라이브러리 추가 (자바는 jdbc 드라이버 필수)

implementation 'org.springframework.boot:spring-boot-starter-jdbc'
runtimeOnly 'com.h2database:h2'

• 스프링 부트 데이터베이스 연결 설정 추가. (resources/application.properties)

spring.datasource.url=jdbc:h2:tcp://localhost/~/test
spring.datasource.driver-class-name=org.h2.Driver
spring.datasource.username=sa

package hello.hellospring.repository;
import hello.hellospring.domain.Member;
import org.springframework.jdbc.datasource.DataSourceUtils;
import javax.sql.DataSource;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

public class JdbcMemberRepository implements MemberRepository {

    private final DataSource dataSource;

    public JdbcMemberRepository(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    @Override
    public Member save(Member member) {
        String sql = "insert into member(name) values(?)";
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = getConnection();
            pstmt = conn.prepareStatement(sql,
                    Statement.RETURN_GENERATED_KEYS);
            pstmt.setString(1, member.getName());
            pstmt.executeUpdate();
            rs = pstmt.getGeneratedKeys();
            if (rs.next()) {
                member.setId(rs.getLong(1));
            } else {
                throw new SQLException("id 조회 실패");
            }
            return member;
        } catch (Exception e) {
            throw new IllegalStateException(e);
        } finally {
            close(conn, pstmt, rs);
        }
    }

    @Override
    public Optional<Member> findById(Long id) {
        String sql = "select * from member where id = ?";
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = getConnection();
            pstmt = conn.prepareStatement(sql);
            pstmt.setLong(1, id);
            rs = pstmt.executeQuery();
            if(rs.next()) {
                Member member = new Member();
                member.setId(rs.getLong("id"));
                member.setName(rs.getString("name"));
                return Optional.of(member);
            } else {
                return Optional.empty();
            }
        } catch (Exception e) {
            throw new IllegalStateException(e);
        } finally {
            close(conn, pstmt, rs);
        }
    }

    @Override
    public List<Member> findAll() {
        String sql = "select * from member";
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = getConnection();
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            List<Member> members = new ArrayList<>();
            while(rs.next()) {
                Member member = new Member();
                member.setId(rs.getLong("id"));
                member.setName(rs.getString("name"));
                members.add(member);
            }
            return members;
        } catch (Exception e) {
            throw new IllegalStateException(e);
        } finally {
            close(conn, pstmt, rs);
        }
    }

    @Override
    public Optional<Member> findByName(String name) {
        String sql = "select * from member where name = ?";
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = getConnection();
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, name);
            rs = pstmt.executeQuery();
            if(rs.next()) {
                Member member = new Member();
                member.setId(rs.getLong("id"));
                member.setName(rs.getString("name"));
                return Optional.of(member);
            }
            return Optional.empty();
        } catch (Exception e) {
            throw new IllegalStateException(e);
        } finally {
            close(conn, pstmt, rs);
        }
    }

    private Connection getConnection() {
        return DataSourceUtils.getConnection(dataSource);
    }

    private void close(Connection conn, PreparedStatement pstmt, ResultSet rs)
    {
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (pstmt != null) {
                pstmt.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (conn != null) {
                close(conn);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    private void close(Connection conn) throws SQLException {
        DataSourceUtils.releaseConnection(conn, dataSource);
    }
}

스프링 설정 변경. (Springconfig 에서 기존에 사용하던 로직 주석처리후 JDBC 로 변경)

package hello.hellospring;

import hello.hellospring.repository.JdbcMemberRepository;
import hello.hellospring.repository.MemberRepository;
import hello.hellospring.repository.MemoryMemberRepository;
import hello.hellospring.service.MemberService;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;

@Configuration
public class SpringConfig {

    private final DataSource dataSource;

    public SpringConfig(DataSource dataSource) {
        this.dataSource = dataSource;
    }

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

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

• DataSource는 데이터베이스 커넥션을 획득할 때 사용하는 객체.
• 스프링 부트는 데이터베이스 커넥션 정보를 바탕으로 DataSource를 생성, 스프링 빈으로 만들어둔다. 그래서 DI를 받을 수 있다.
• 개방-폐쇄 원칙(OCP, Open-Closed Principle) : 확장에는 열려있고, 수정, 변경에는 닫혀있다.
• 스프링의 DI (Dependencies Injection) 사용 시, 기존 코드를 손대지 않고, 설정만으로 구현 클래스를 변경할 수 있다.