// 接口
    List<SysUser> findByIdList(List<Integer> idList);

    //xml
    <select id="findByIdList" resultMap="BaseResultMap">
        SELECT *
        FROM sys_user
        <where>
            <if test="list!= null and list.size() > 0">
                id IN
                <foreach collection="list" item="item" index="index" open="(" separator="," close=")">
                    #{item}
                </foreach>
            </if>
        </where>
    </select>