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RowMapper

RowMapper maps each row when reading a ResultSet. You do not need to manage the ResultSet traversal—just focus on converting each row's data.

Interface Definition

@FunctionalInterface
public interface RowMapper<T> {
    T mapRow(ResultSet rs, int rowNum) throws SQLException;
}

Custom Implementation Example

public class UserRowMapper implements RowMapper<User> {
    public User mapRow(ResultSet rs, int rowNum) throws SQLException {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setName(rs.getString("name"));
        return user;
    }
}

How to Use

Example: Programmatic API

UserRowMapper userRowMapper = new UserRowMapper();
List<User> result = jdbc.queryForList("select * from users", userRowMapper);

Example: Declarative API

@SimpleMapper
public interface UserMapper {
    @Query(value = "select * from users where id > #{id}",
           resultRowMapper = UserRowMapper.class)
    List<User> listUsers(@Param("id") long searchId);
}

Example: Fluent API

List<User> result = lambda.query(User.class)
                          .le(User::getId, 100)
                          .queryForList(userRowMapper);

Example: Mapper File

<select id="queryListByAge" resultRowMapper="com.example.dto.UserRowMapper">
    select * from users where age = #{age}
</select>

Built-ins

dbVisitor ships with 5 built-in RowMapper implementations; you can extend further as needed.

ColumnMapRowMapper

// Convert each row to Map<String, Object>, suitable for any query
String querySql = "select * from users where age > 40";
RowMapper<Map<String, Object>> rowMapper = new ColumnMapRowMapper();
List<Map<String, Object>> result = jdbc.queryForList(querySql, rowMapper);

SingleColumnRowMapper

// When the query result has only one column, convert directly to target type
String querySql = "select name from users where age > 40";
RowMapper<String> rowMapper = new SingleColumnRowMapper<>(String.class);
List<String> result = jdbc.queryForList(querySql, rowMapper);

BeanMappingRowMapper

// Map each row to a Bean based on ORM mapping
String querySql = "select * from users where age > 40";
RowMapper<TestUser> rowMapper = new BeanMappingRowMapper<>(TestUser.class);
List<TestUser> result = jdbc.queryForList(querySql, rowMapper);

MapMappingRowMapper

// Map each row to a Map based on ORM mapping (only includes declared mapped columns)
String querySql = "select * from users where age > 40";
RowMapper<Map<String, Object>> rowMapper = new MapMappingRowMapper<>(TestUser.class);
List<Map<String, Object>> result = jdbc.queryForList(querySql, rowMapper);

TypeHandlerColumnRowMapper

// When the query result has only one column, use a specified TypeHandler for type conversion
String querySql = "select create_time from users where age > 40";
RowMapper<LocalDateTime> rowMapper = new TypeHandlerColumnRowMapper<>(new LocalDateTimeOfTimestampTypeHandler());
List<LocalDateTime> result = jdbc.queryForList(querySql, rowMapper);

Difference between ColumnMapRowMapper and MapMappingRowMapper

Both return Map, but behave differently:

• ColumnMapRowMapper — Puts all columns returned by the query into the Map, suitable for select * and any arbitrary queries.
• MapMappingRowMapper — Based on the entity type from its constructor, only retains columns declared in ORM mapping; extra queried columns are ignored.