토비의 스프링-DAO-(3)

인터페이스의 도입

• 중간에 추상적인 연결고리를 만든다.
• 인터페이스를 이용
  • 인터페이스는 어떤 일을 하겠다는 기능만 정의 해놓은 것으로, 인터페이스를 구현한 클래스가 세부 기능을 결정한다.

public interface Connectionmaker {
    public Connection make connection() throws ClassNotFoundException,SQLException;
}
public class MysqlConnectionMaker implements ConnectionMaker {
    public Connection makeConnection() throws ClassNotFoundException,SQLEception {
        Class.forName("com.mysql.jdbc.Driver");
        Connection c = DriverManager.getConnection("jdbc:mysql://localhost/DBname","ID","PW");
        return c;
    }
}
public class MariadbConnectionMaker implements ConnectionMaker {
    public Connection makeConnection() throws ClassNotFOoundException,SQLEception {
        Class.forName("org.mariadb.jdbc.Driver");
        Connection c = DriverManager.getConnection("jdbc:mariadb://localhost/DBname","ID","PW");
        return c;
    }
}

public class UserDao {
    private SimpleConnectionMaker simpleConnectionMaker;
    public UserDao() {
        simpleConnectionMaker = new MysqlConnectionMaker();
        //simpleConnectionMaker = new MariadbConnectionMaker();
    }
    public void add(user user) throws ClassNotFoundException, SQLException {
        Connection c = simpleConnectionMaker.makeNewConnection();
        PreparedStatement ps = c.prepareStatement("insert into users(id,name,password)values(?,?,?)");
        ps.setString(1,user.getId());
        ps.setString(2,user.getName());
        ps.setString(3,user.getPassword());

        ps.executeUpdate();

        ps.close();
        c.close();
    }
    public User get(String id) throws ClassNotFoundException,SQLException {
        Connection c = simpleConnectionMaker.makeNewConnection();
        PreparedStatement ps = c.prepareStatment("select * from users where id = ?");
        ps.setString(1,id);

        ResultSet rs = ps.executeQuery();
        rs.next();
        User user = new User();
        user.setId(rs.getString("id"));
        user.setName(rs.getString("name"));
        user.setPassword(rs.getString("password"));

        rs.close();
        ps.close();
        c.close();

        return user;
    }
}

• UserDao 클래스에 전용 클래스를 기술해야한다 --> 전용 클래스 수정시 내부 클래스도 수정해야하는 단점 여전히 가짐
• 확장성 불가

관계설정 책임의 분리

• 그렇다면 다른 부분에서 관계설정을 하게끔 해준다면 UserDao 클래스의 수정은 필요없어진다.
• 생성자를 이용하여 분리

public class UserDao {
    private ConnectionMaker connectionMaker;
    public UserDao(ConnectionMaker connectionMaker) {
        this.connectionMaker = connectionMaker;
    }

    public void add(user user) throws ClassNotFoundException, SQLException {
        Connection c = connectionMaker.makeNewConnection();
        PreparedStatement ps = c.prepareStatement("insert into users(id,name,password)values(?,?,?)");
        ps.setString(1,user.getId());
        ps.setString(2,user.getName());
        ps.setString(3,user.getPassword());
        ps.executeUpdate();
        ps.close();
        c.close();
    }
    
    public User get(String id) throws ClassNotFoundException,SQLException {
        Connection c = connectionMaker.makeNewConnection();
        PreparedStatement ps = c.prepareStatment("select * from users where id = ?");
        ps.setString(1,id);

        ResultSet rs = ps.executeQuery();
        rs.next();
        User user = new User();
        user.setId(rs.getString("id"));
        user.setName(rs.getString("name"));
        user.setPassword(rs.getString("password"));

        rs.close();
        ps.close();
        c.close();

        return user;
    }
}

public class UserDaoTest {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        ConnectionMaker connectionMaker = new MysqlConnectionMaker();
        UserDao dao = new UserDao(connectionMaker);
        //...
    }
}