/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jdbc.core;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import org.springframework.util.Assert;

Adapter implementation of the ResultSetExtractor interface that delegates
to a RowMapper which is supposed to create an object for each row.
Each object is added to the results List of this ResultSetExtractor.
Useful for the typical case of one object per row in the database table.
The number of entries in the results list will match the number of rows.
Note that a RowMapper object is typically stateless and thus reusable;
just the RowMapperResultSetExtractor adapter is stateful.
A usage example with JdbcTemplate:
JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);  // reusable object
RowMapper rowMapper = new UserRowMapper();  // reusable object
List allUsers = (List) jdbcTemplate.query(
    "select * from user",
    new RowMapperResultSetExtractor(rowMapper, 10));
User user = (User) jdbcTemplate.queryForObject(
    "select * from user where id=?", new Object[] {id},
    new RowMapperResultSetExtractor(rowMapper, 1));
Alternatively, consider subclassing MappingSqlQuery from the jdbc.object package: Instead of working with separate JdbcTemplate and RowMapper objects, you can have executable query objects (containing row-mapping logic) there. 
Author:
Juergen Hoeller
Type parameters:
<T> – the result element type
See Also:
RowMapper
JdbcTemplate
MappingSqlQuery
Since:
1.0.2/**
 * Adapter implementation of the ResultSetExtractor interface that delegates
 * to a RowMapper which is supposed to create an object for each row.
 * Each object is added to the results List of this ResultSetExtractor.
 *
 * <p>Useful for the typical case of one object per row in the database table.
 * The number of entries in the results list will match the number of rows.
 *
 * <p>Note that a RowMapper object is typically stateless and thus reusable;
 * just the RowMapperResultSetExtractor adapter is stateful.
 *
 * <p>A usage example with JdbcTemplate:
 *
 * <pre class="code">JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);  // reusable object
 * RowMapper rowMapper = new UserRowMapper();  // reusable object
 *
 * List allUsers = (List) jdbcTemplate.query(
 *     "select * from user",
 *     new RowMapperResultSetExtractor(rowMapper, 10));
 *
 * User user = (User) jdbcTemplate.queryForObject(
 *     "select * from user where id=?", new Object[] {id},
 *     new RowMapperResultSetExtractor(rowMapper, 1));</pre>
 *
 * <p>Alternatively, consider subclassing MappingSqlQuery from the {@code jdbc.object}
 * package: Instead of working with separate JdbcTemplate and RowMapper objects,
 * you can have executable query objects (containing row-mapping logic) there.
 *
 * @author Juergen Hoeller
 * @since 1.0.2
 * @param <T> the result element type
 * @see RowMapper
 * @see JdbcTemplate
 * @see org.springframework.jdbc.object.MappingSqlQuery
 */
public class RowMapperResultSetExtractor<T> implements ResultSetExtractor<List<T>> {

	private final RowMapper<T> rowMapper;

	private final int rowsExpected;


	
Create a new RowMapperResultSetExtractor.
Params:
rowMapper – the RowMapper which creates an object for each row/**
	 * Create a new RowMapperResultSetExtractor.
	 * @param rowMapper the RowMapper which creates an object for each row
	 */
	public RowMapperResultSetExtractor(RowMapper<T> rowMapper) {
		this(rowMapper, 0);
	}

	
Create a new RowMapperResultSetExtractor.
Params:
rowMapper – the RowMapper which creates an object for each row
rowsExpected – the number of expected rows
(just used for optimized collection handling)/**
	 * Create a new RowMapperResultSetExtractor.
	 * @param rowMapper the RowMapper which creates an object for each row
	 * @param rowsExpected the number of expected rows
	 * (just used for optimized collection handling)
	 */
	public RowMapperResultSetExtractor(RowMapper<T> rowMapper, int rowsExpected) {
		Assert.notNull(rowMapper, "RowMapper is required");
		this.rowMapper = rowMapper;
		this.rowsExpected = rowsExpected;
	}


	@Override
	public List<T> extractData(ResultSet rs) throws SQLException {
		List<T> results = (this.rowsExpected > 0 ? new ArrayList<>(this.rowsExpected) : new ArrayList<>());
		int rowNum = 0;
		while (rs.next()) {
			results.add(this.rowMapper.mapRow(rs, rowNum++));
		}
		return results;
	}

}