Mybatis--代理开发

目的：解决原生方式中的硬编码；简化后期执行SQL

步骤：
1.定义与sql映射文件同名的Mapper接口，并且将Mapper接口和SQL映射文件放置在同一目录下(创建多级目录时将.替换为/)

屏幕截图 2022-06-20 180832.png

2.设置SQL映射文件的namespace属性为Mapper接口全限定名
<?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">
<!--namespace:名称空间-->
<mapper namespace="Mapper.UserMapper">
    <select id="selectAll" resultType="pojo.User">
        select * from tb_user;
    </select>
</mapper>

3.在Mapper接口中定义方法，方法名是SQL映射文件中SQL语句的id，并保持参数类型和返回值类型一致
package Mapper;

import pojo.User;

import java.util.List;

public interface UserMapper {

    List<User> selectAll();
}

4.编码
①通过sqlSession的getMapper方法获取Mapper接口的代理对象
②调用对应方法完成SQL执行
import Mapper.UserMapper;
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 pojo.User;

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

/**
 代理开发
 */

public class MybatisDemo2 {
    public static void main(String[] args) throws IOException {
        //加载mybatis的核心配置文件,获取sqlSessionFactory
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        //获取sqlSession对象用它执行sql
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //执行sql
//        List<User> users = sqlSession.selectList("test.selectAll");
        //获取UserMapper接口的代理对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = userMapper.selectAll();

        System.out.println(users);

        sqlSession.close();
    }
}