Jdbc(Java DataBase Connectivity) Template

オープンクローズの原則

@Configuration
public class SpringConfig {

    // skipped parts(D.I parts from Spring Container)
    
    @Bean
    public MemberRepository memberRepository() {
        // return new MemoryMemberRepository();
        return new JdbcTemplateMemberRepository(dataSource); // OCP(open-closed principle)
    }
}

Initalize JdbcTemplate

public class JdbcTemplateMemberRepository implements MemberRepository {

    private final JdbcTemplate jdbcTemplate;

    @Autowired // annotation may be skipped if there's only one constructor.
    public JdbcTemplateMemberRepository(DataSource dataSource) {
        jdbcTemplate = new JdbcTemplate(dataSource);
    }
    + Implementation of Interface as of here.
    .
    .
    .
}

SimpleJdbcInsert

 @Override
    public Member save(Member member) {

	// initialize instance and set parameter.
        SimpleJdbcInsert jdbcInsert = new SimpleJdbcInsert(jdbcTemplate);
        jdbcInsert.withTableName("member").usingGeneratedKeyColumns("id");

	// Map parameters to pass in the actual execution.
        Map<String, Object> parameters = new HashMap<>(); // Object class as a generic type.
        parameters.put("name", member.getName());

        Number key = jdbcInsert.executeAndReturnKey(new MapSqlParameterSource(parameters));
        member.setId(key.longValue());

        return member;
    }

findById(), findByName(), findAll()

@Override
    public Optional<Member> findById(Long id) {
        List<Member> result = jdbcTemplate.query("select * from member where id = ?",
                memberRowMapper(), id);
        return result.stream().findAny();
    }

    @Override
    public List<Member> findAll() {
        return jdbcTemplate.query("select * from member", memberRowMapper());
    }

    @Override
    public Optional<Member> findByName(String name) {
        List<Member> result = jdbcTemplate.query("select * from member where name = ?",
                memberRowMapper(), name);
        return result.stream().findAny();
    }

lambda of RowMapper Interface

private RowMapper<Member> memberRowMapper() {
        return (rs, rowNum) -> {
            Member member = new Member();
            member.setId(rs.getLong("id"));
            member.setName(rs.getString("name"));
            return member;
        };
    }

JdbcTemplateMemberRepository.java

public class JdbcTemplateMemberRepository implements MemberRepository {

    private final JdbcTemplate jdbcTemplate;

    @Autowired // annotation may be skipped if there's only one constructor.
    public JdbcTemplateMemberRepository(DataSource dataSource) {
        jdbcTemplate = new JdbcTemplate(dataSource);
    }

    @Override
    public Member save(Member member) {

        SimpleJdbcInsert jdbcInsert = new SimpleJdbcInsert(jdbcTemplate);
        jdbcInsert.withTableName("member").usingGeneratedKeyColumns("id");

        Map<String, Object> parameters = new HashMap<>(); // Object class as a generic type.
        parameters.put("name", member.getName());

        Number key = jdbcInsert.executeAndReturnKey(new MapSqlParameterSource(parameters));
        member.setId(key.longValue());

        return member;
    }

    @Override
    public Optional<Member> findById(Long id) {
        List<Member> result = jdbcTemplate.query("select * from member where id = ?",
                memberRowMapper(), id);
        return result.stream().findAny();
    }

    @Override
    public List<Member> findAll() {
        return jdbcTemplate.query("select * from member", memberRowMapper());
    }

    @Override
    public Optional<Member> findByName(String name) {
        List<Member> result = jdbcTemplate.query("select * from member where name = ?",
                memberRowMapper(), name);
        return result.stream().findAny();
    }

    private RowMapper<Member> memberRowMapper() {
        return (rs, rowNum) -> {
            Member member = new Member();
            member.setId(rs.getLong("id"));
            member.setName(rs.getString("name"));
            return member;
        };
    }
}