mybatis判断集合为空或者元素个数为零：
<if test="mlhs != null and mlhs.size() != 0"> and t.mlh_name not in <foreach collection="mlhs" item="item1" open="(" close=")" index="i" separator=","> #{item1,jdbcType=VARCHAR} </foreach> </if>
原文：http://www.cnblogs.com/stono/p/4941585.html