MyBatis标签获取数组或集合长度的实现方式

<if test="list != null and list.size() > 0">
  ...
</if>
可结合in条件使用：
 select * from users
  <where>
    <if test="idlist != null and idlist.size() > 0">
      id in
      <foreach item="item" index="index" collection="idlist" open="(" separator="," close=")">
        #{item}
      </foreach>
    </if>
  </where>

<if test="array != null and array.length > 0">
  ...
</if>

${list[0]}
${array[0]}