mybatis学习（三）——接口式编程

对于上一节中的查询我们还可以通过接口的方式进行编程，开发环境和上一节一样

1、全局配置文件mybatis_config.xml（和上一节一样）

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <!-- 配置数据库源信息 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/spring_mybatis" />
                <property name="username" value="root" />
                <property name="password" value="pjf520" />
            </dataSource>
        </environment>
    </environments>
</configuration>

2、JAVA代码实体类（和上一节一样）

package com.pjf.mybatis.po;

public class Hotel {
    private int hotelId;
    private String hotelName;
    private String hotelAddress;
    private int price;

    public int getHotelId() {
        return hotelId;
    }

    public void setHotelId(int hotelId) {
        this.hotelId = hotelId;
    }

    public String getHotelName() {
        return hotelName;
    }

    public void setHotelName(String hotelName) {
        this.hotelName = hotelName;
    }

    public String getHotelAddress() {
        return hotelAddress;
    }

    public void setHotelAddress(String hotelAddress) {
        this.hotelAddress = hotelAddress;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Hotel [hotelId=" + hotelId + ", hotelName=" + hotelName + ", hotelAddress=" + hotelAddress + ", price="
                + price + "]";
    }

}

3、（新增）编写hotelMapper接口

package com.pjf.mybatis.dao;

import com.pjf.mybatis.po.Hotel;

public interface HotelMapper {

    public Hotel getHotel(Integer i);
}

4、（修改）编写sql映射文件hotelMapper.xml

这里修改了namespace，定义为接口的类全名，上一节这里可以随便写。

然后修改了sql的id，对应到接口中的方法，这样xml和接口就一一对应了

<?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" >
<!-- 这里的namespace写hotelMapper接口的类全名，和接口一一对应 -->
<mapper namespace="com.pjf.mybatis.dao.HotelMapper">

    <!-- 这里的id写hotelMapper接口对应的方法名 -->
    <select id="getHotel" resultType="com.pjf.mybatis.po.Hotel">
        select id,hotel_name as
        hotelName, hotel_address as hotelAddress, price from hotel
        where
        id=#{id}
    </select>

</mapper>

5、（修改）编写测试类

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;
    }

    @Test
    public void getHotel() throws IOException {
        //如果有多个会话，会新建多个SqlSessionFactory，将重复的内容通过函数提取出来了
        SqlSessionFactory sessionFactory = sqlSessionFactory();
        // 打开jdbc会话
        SqlSession session = sessionFactory.openSession();
        // 创建hotelMapper类的实例
        // 虽然这是个接口，但是mybatis会通过动态代理新建一个实体类
        // 可以通过System.out.println(hotelMapper.getClass())查看该类的类型
        // 输出class com.sun.proxy.$Proxy5，可以看到是一个代理类
        HotelMapper hotelMapper = session.getMapper(HotelMapper.class);
        System.out.println(hotelMapper.getClass());

        Hotel hotel = hotelMapper.getHotel(1001);
        System.out.println(hotel);
        session.close();
    }
}

可以看到结果和之前一致。