本章节将介绍怎样使用 <select> 标签的 resultType 属性来指定返回结果类型，例如：统计总数量返回 Integer、数据行返回 HashMap（后面将介绍返回 JavaBean）。
（1）MyBatis 配置 mybatis-cfg.xml 文件如下：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="database.properties"/>
<environments default="MySqlDatabase" >
<environment id="MySqlDatabase" >
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<!-- 加载我们定义的Mapper文件 -->
<mapper resource="com/hxstrive/mybatis/select/demo1/UserMapper.xml" />
</mappers>
</configuration>上面配置只是简单的配置了数据源和Mapper文件资源。
（2）Mapper 接口 UserMapper.java，如下：
package com.hxstrive.mybatis.select.demo1;
import org.apache.ibatis.annotations.Param;
import java.util.Map;
public interface UserMapper {
/** 根据ID查询用户信息 */
Map<String,Object> getUserById(@Param("userId") int userId);
/** 查询用户数 */
int getUserCount();
}（3）Mapper XML文件 UserMapper.xml，如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hxstrive.mybatis.select.demo1.UserMapper">
<!-- 根据ID查询用户信息 -->
<select id="getUserById" parameterType="int" resultType="hashmap">
select `user_id`, `name`, `sex`, `age`
from `user`
where `user_id`=#{userId,jdbcType=INTEGER}
</select>
<!-- 查询用户数 -->
<select id="getUserCount" resultType="integer">
select count(*) from `user`
</select>
</mapper>（4）客户端，如下：
package com.hxstrive.mybatis.select.demo1;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.InputStream;
import java.util.Map;
public class SelectDemo1 {
public static void main(String[] args) throws Exception {
String cfgName = "com/hxstrive/mybatis/select/demo1/mybatis-cfg.xml";
InputStream input = Resources.getResourceAsStream(cfgName);
SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlFactory = factoryBuilder.build(input);
SqlSession sqlSession = sqlFactory.openSession(true);
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
// 根据用户ID获取用户信息
Map<String,Object> userMap = userMapper.getUserById(1);
for(String key : userMap.keySet()) {
System.out.println(key + "=" + userMap.get(key));
}
// 获取用户数量
int userCount = userMapper.getUserCount();
System.out.println("用户总数=" + userCount);
}
}运行结果：
user_id=1 sex=男 name=张三 age=28 用户总数=2
