OrderRepository.java

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowMapper;
import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.Optional;

@Repository
public class OrderRepository {
    private static final RowMapper<Order> rowMapper = (rs, i) -> new Order(rs.getLong("id"));
    private final JdbcTemplate jdbcTemplate;

    public OrderRepository(final JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }
    
    public Optional<Order> findOrderById(Long id) {
        List<Order> query = jdbcTemplate.query("select * from orders where id=:id", rowMapper, id);
        if (query.size() > 1) throw new RuntimeException("Too many results from findOrderById.");
        return query.size() == 1 ? Optional.of(query.get(0)) : Optional.empty();
    }
}