OnlineJudge/src/main/resources/mapper/userMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.onlinejudge.mapper.UserMapper">
    <select id="selectUserById" resultType="com.example.onlinejudge.model.entity.User">
        SELECT * FROM t_user WHERE id = #{id}
    </select>
    <select id="selectUserByUsernameAndPassword" resultType="com.example.onlinejudge.model.entity.User">
        SELECT * FROM t_user WHERE username = #{param1} and password = #{param2}
    </select>
</mapper>