-- mapper
    void updateBatch(@Param("list") List<User> users);
--- sql
    <update id="updateBatch">
        update user
        set
        name =
        <foreach collection="list" item="item" open="case id" index="index" separator="" close="end">
        when #{item.id} then #{item.name}
    </foreach>,
        age =
        <foreach collection="list" item="item" open="case id" index="index" separator="" close="end">
            when #{item.id} then #{item.age}
        </foreach>
        where
        id in
        <foreach collection="list" item="item" open="(" index="index" separator="," close=")">
            #{item.id}
        </foreach>
    </update>
总结：
1.通过case id 来保证foreach中循环的是同一个对象，在set和where条件中，从而达到批量更新