出现此异常是因为返回的数据类型不对应
错误示范
dao层代码片
public List<student> insertgradesex(student stu);
对应的Mapper代码片
<select id="insertgradesex">
select * from
stuinfo
where 1=1
<if test="sex!=null and sex!=''">
and sex = #{sex}
</if>
<if test="grade!=null and grade!=''">
and grade = #{grade}
</if>
</select>
更正
<select id="insertgradesex" parameterType="student" resultType="student">
select * from
stuinfo
where 1=1
<if test="sex!=null and sex!=''">
and sex = #{sex}
</if>
<if test="grade!=null and grade!=''">
and grade = #{grade}
</if>
</select>
异常解决