gold-java/src/main/resources/mapper/UrlMapper.xml

<?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">
<mapper namespace="com.example.demo.mapper.UrlMapper">

    <select id="selectBaseUrl" resultType="java.lang.String">
        select value from env where `key` = #{key}
    </select>
</mapper>