MyBatis异常处理org.apache.ibatis.executor.ExecutorException报错：A query was run and no Result Maps were fo

今天在学习MyBatis是遇见了一个报错，记录下来。
在我配置好核心文件和映射文件并在会话工厂执行时出现了：MyBatis异常处理org.apache.ibatis.executor.ExecutorException并提示：
A query was run and no Result Maps were found for the Mapped Statement意思大概是：使用mybatis进行查询时，没有给定resultType值出现的错误。resultType是查询对象的类型

排查后发现是因为没有在映射文件指明查询结果的返回值类型：resultType的值，
我这里返回的是int类型，修改后再运行就没有问题了。

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="TeacherMapper">
<select id="countTeacher"  resultType="int">
select count(*) from teacher
</select>
</mapper>