按主键查学生mapper.xml实现

MyBatis typeAliases（别名)

UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="us">
    <!--
        按主键id查询学生信息
        Student getAll(Integer id);
        有没有入参(传入的参数)?有parameterType,里面是有别名机制的
        有没有返回值?有就resultType
    -->
    <select id="getById" parameterType="int" resultType="org.pojo.Student">
        select * from student where id=#{id}
    </select>
</mapper>

修改主配置文件

<?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>
    ....
        <mapper resource="UserMapper.xml"></mapper>
    </mappers>
</configuration>

测试功能

public class AppTest{
    @Test
    public void testGetById() throws IOException {
        //读取配置文件信息
        InputStream in = Resources.getResourceAsStream("mybatis.xml");
        //创建SqlSessionFactory对象
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        //取出SqlSession
        SqlSession sqlSession = factory.openSession();
        //按主键查学生
        List<Student> list = sqlSession.selectList("us.getById",1001);//注意这条
        list.forEach(student -> System.out.println(student));
        //关闭SqlSession
        sqlSession.close();
    }
}