mybatis 学习笔记（三）：mapper 代理开发 dao 层

<?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 命名空间，作用就是对sql进行分类化管理,理解为sql隔离
 注意：使用mapper代理方法开发，namespace有特殊重要的作用
 namespace等于 mapper 接口地址
 -->
<mapper namespace="cn.itcast.mybatis.mapper.UserMapper">
    <select id="findUserById" parameterType="int" resultType="cn.itcast.mybatis.po.User">
        SELECT * FROM USER WHERE id=#{value}
    </select>
</mapper>

package cn.itcast.mybatis.mapper;

import cn.itcast.mybatis.po.User;

import java.util.List;

public interface UserMapper {

    //根据 id 查询用户信息
    public User findUserById(int id) throws Exception;

}

    <!-- 加载映射文件 -->
    <mappers>
        <!-- 通过 resource 方法一次加载一个映射文件 -->
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>

package cn.itcast.mybatis.mapper;

import cn.itcast.mybatis.po.User;
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.Before;
import org.junit.Test;

import java.io.InputStream;

public class UserMapperTest {

    private SqlSessionFactory sqlSessionFactory;

    //注解Before是在执行本类所有测试方法之前先调用这个方法
    @Before
    public void setup() throws Exception{
        //创建SqlSessionFactory
        String resource="SqlMapConfig.xml";

        //将配置文件加载成流
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //创建会话工厂，传入mybatis配置文件的信息
        sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
    }


    @Test
    public void testFindUserById() throws Exception{

        SqlSession sqlSession=sqlSessionFactory.openSession();

        //创建UserMapper代理对象
        UserMapper userMapper=sqlSession.getMapper(UserMapper.class);

        //调用userMapper的方法
        User user=userMapper.findUserById(1);

        sqlSession.close();

        System.out.println(user);
    }
}