① 首先查看mapper接口跟mapper.xml的映射关系
② 是否加了注解@MapperScan
③ mapper-locations是否配置正确
④ 如果xml文件是放在src/main/java下
需在 pom.xml 下配置
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
</includes>
</resource>
</resources>
</build>