mybatis学习（七）——resultType解析

resultType是sql映射文件中定义返回值类型，返回值有基本类型，对象类型，List类型，Map类型等。现总结一下再解释

总结：

resultType:

1、基本类型  ：resultType=基本类型

2、List类型：   resultType=List中元素的类型

3、Map类型    单条记录：resultType =map

                          多条记录：resultType =Map中value的类型

1、对象类型

对于对象类型resultType直接写对象的全类名就可以了

实例：

hotelMapper接口

package com.pjf.mybatis.dao;

import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {
    //返回值类型为Hotel
    public Hotel getHotel(Integer i);

}

HotelMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.pjf.mybatis.dao.HotelMapper">
    <!--resultType直接写对象的全类名 -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select * from hotel
        where
        id=#{id}
    </select>
</mapper>

测试类：

package com.pjf.mybatis;

import java.io.IOException;
import java.io.InputStream;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 org.junit.Test;

import com.pjf.mybatis.dao.HotelMapper;
import com.pjf.mybatis.po.Hotel;

public class TestHotel {

    public SqlSessionFactory sqlSessionFactory() throws IOException {
        // mybatis的配置文件
        String resource = "mybatis_config.xml";
        // 使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）TestHotel.class.getClassLoader()
        InputStream is = Resources.getResourceAsStream(resource);
        // 构建sqlSession的工厂
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        return sessionFactory;
    }
    // 查
    @Test
    public void getHotel() throws IOException {

        SqlSessionFactory sessionFactory = sqlSessionFactory();
        SqlSession session = sessionFactory.openSession();
        HotelMapper hotelMapper = session.getMapper(HotelMapper.class);
        System.out.println(hotelMapper.getClass());
        //直接返回Hotel对象，打印出来        
        Hotel hotel = hotelMapper.getHotel(1001);
        System.out.println(hotel);
        session.close();
    }

}

2、List类型

返回值为List类型，resultType为List中对象的类型，如List<Hotel>，resultType为Hotel

实例：

hotelMapper接口

package com.pjf.mybatis.dao;

import java.util.List;

import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {
    // 返回值为List
    public List<Hotel> getHotel(Integer i);
}

hotelMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.pjf.mybatis.dao.HotelMapper">
    <!-- 返回值为List，resultType为List中元素的全类名 -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select * from hotel
        where
        price>#{price}
    </select>
</mapper>

测试类

package com.pjf.mybatis;

import java.io.IOException;
import java.io.InputStream;

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 org.junit.Test;

import com.pjf.mybatis.dao.HotelMapper;
import com.pjf.mybatis.po.Hotel;

public class TestHotel {

    public SqlSessionFactory sqlSessionFactory() throws IOException {
        // mybatis的配置文件
        String resource = "mybatis_config.xml";
        // 使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）TestHotel.class.getClassLoader()
        InputStream is = Resources.getResourceAsStream(resource);
        // 构建sqlSession的工厂
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        return sessionFactory;
    }

    // 查
    @Test
    public void getHotel() throws IOException {

        SqlSessionFactory sessionFactory = sqlSessionFactory();
        SqlSession session = sessionFactory.openSession();
        HotelMapper hotelMapper = session.getMapper(HotelMapper.class);
        System.out.println(hotelMapper.getClass());
        // 返回值为List
        List<Hotel> list = hotelMapper.getHotel(1000);
        for (Hotel hotel : list) {
            System.out.println(hotel);
        }
        session.close();
    }
}

3、Map类型

a、返回单条记录的map，key为属性，值为属性值。resultType为map

hotelMapper接口

package com.pjf.mybatis.dao;

import java.util.Map;
import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {
    // 返回值为Map，key为属性名，value为属性值
    public Map<String, Object> getHotel(Integer i);
}

hotelMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.pjf.mybatis.dao.HotelMapper">
    <!-- 返回值为map，resultType为map -->
    <select id="getHotel" resultType="map">
        select * from hotel
        where
        id=#{id}
    </select>
</mapper>

测试类，返回id=1001的酒店

package com.pjf.mybatis;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;

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 org.junit.Test;

import com.pjf.mybatis.dao.HotelMapper;
import com.pjf.mybatis.po.Hotel;

public class TestHotel {

    public SqlSessionFactory sqlSessionFactory() throws IOException {
        // mybatis的配置文件
        String resource = "mybatis_config.xml";
        // 使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）TestHotel.class.getClassLoader()
        InputStream is = Resources.getResourceAsStream(resource);
        // 构建sqlSession的工厂
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        return sessionFactory;
    }

    // 查
    @Test
    public void getHotel() throws IOException {

        SqlSessionFactory sessionFactory = sqlSessionFactory();
        SqlSession session = sessionFactory.openSession();
        HotelMapper hotelMapper = session.getMapper(HotelMapper.class);
        System.out.println(hotelMapper.getClass());
        // 返回值为map
        Map<String, Object> map = hotelMapper.getHotel(1001);
        System.out.println(map);
        session.close();
    }
}

b、返回多条记录的map，key为任意一属性，值为对象类型。如Map<String,Hotel>,resultType为Hotel

返回多条记录的map时，key为任意一属性，值为对象类型，不过key需要通过@MapKey("hotelName")指定对象中一个属性名为key

实例：

hotelMapper接口

package com.pjf.mybatis.dao;

import java.util.Map;
import org.apache.ibatis.annotations.MapKey;

import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {
    // 返回值为Map，key需要通过@MapKey("属性名")来指定javaBean中的一个属性名为key，value为对象
    @MapKey("hotelName")
    public Map<String, Hotel> getHotel(Integer i);
}

hotelMapper.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.pjf.mybatis.dao.HotelMapper">
    <!-- 返回值为map，resultType为对象的全类名 -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select * from hotel
        where
        price>#{price}
    </select>
</mapper>

测试类：返回价格>1000以上的酒店

package com.pjf.mybatis;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;

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 org.junit.Test;

import com.pjf.mybatis.dao.HotelMapper;
import com.pjf.mybatis.po.Hotel;

public class TestHotel {

    public SqlSessionFactory sqlSessionFactory() throws IOException {
        // mybatis的配置文件
        String resource = "mybatis_config.xml";
        // 使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）TestHotel.class.getClassLoader()
        InputStream is = Resources.getResourceAsStream(resource);
        // 构建sqlSession的工厂
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        return sessionFactory;
    }

    // 查
    @Test
    public void getHotel() throws IOException {

        SqlSessionFactory sessionFactory = sqlSessionFactory();
        SqlSession session = sessionFactory.openSession();
        HotelMapper hotelMapper = session.getMapper(HotelMapper.class);
        System.out.println(hotelMapper.getClass());
        // 返回值为map
        Map<String, Hotel> map = hotelMapper.getHotel(1000);
        System.out.println(map);
        session.close();
    }
}