Demo :: Refactoring DAO

executeQuery.java

public List<T> executeQuery(String sql, Object[] params, RowMapper<T> rowMapper) throws SQLException{
	List<T> results = new ArrayList<T>();
	ResultSet resultSet = getResultSet(sql, params);
	while(resultSet.next()) {
		results.add(rowMapper.mapRow(resultSet));
	}
	return results;
}

getAll.java

public List<Person> getAll() {
	List<Person> allPerson = new ArrayList<Person>();
	try {
		Connection connection = this.dataSource.getConnection();
		PreparedStatement prep = connection.prepareStatement("select * from person");
		ResultSet resultSet = prep.executeQuery();

		while (resultSet.next()) {
			Person person = new Person();
			person.setID(resultSet.getInt("ID"));
			person.setFirstName(resultSet.getString("FIRSTNAME"));
			allPerson.add(person);
		}
	} catch (Exception e) {
		throw new RuntimeException("Cat not get all person");
	}
	return allPerson;
}

getAll2.java

public List<Person> getAll() {
	try {
		String sql = "select * from person";
		JdbcTemplate<Person> jdbcTemplate = new JdbcTemplate<Person>(this.dataSource);
		return jdbcTemplate.executeQuery(sql, null, new PersonRowMapper());
	} catch (Exception e) {
		throw new RuntimeException("Cat not get all person");
	}
}

getPerson.java

public Person getPerson(int id) {
	Person person = null;
	try {
		Connection connection = this.dataSource.getConnection();
		PreparedStatement prep = connection.prepareStatement("select * from person where id=?");
		prep.setInt(1, id);
		ResultSet resultSet = prep.executeQuery();

		if (resultSet.next()) {
			person = new Person();
			person.setID(resultSet.getInt("ID"));
			person.setFirstName(resultSet.getString("FIRSTNAME"));
		}
	} catch (Exception e) {
		e.printStackTrace();
	}
	return person;
}

getPerson2.java

public Person getPerson(int id) {
	Person person = null;
	try {
		Connection connection = this.dataSource.getConnection();
		PreparedStatement prep = connection.prepareStatement("select * from person where id=?");
		prep.setInt(1, id);
		ResultSet resultSet = prep.executeQuery();

		if (resultSet.next()) {
			person = mappingPerson(resultSet);
		}
	} catch (Exception e) {
		e.printStackTrace();
	}
	return person;
}

mappingPerson.java

private Person mappingPerson(ResultSet resultSet) throws Exception{
	Person person = new Person();
	person.setID(resultSet.getInt("ID"));
	person.setFirstName(resultSet.getString("FIRSTNAME"));
	return person;
}

PersonRowMapper.java

public class PersonRowMapper extends RowMapper<Person> {

	@Override
	public Person mapRow(ResultSet resultSet) throws SQLException {
		Person person = new Person();
		person.setID(resultSet.getInt("ID"));
		person.setFirstName(resultSet.getString("FIRSTNAME"));
		return person;
	}
	
}

RowMapper.java

public abstract class RowMapper<T> {
	
	public abstract T mapRow(ResultSet resultSet) throws SQLException;

}