目录结构如下图：

mapper映射配置：

<mappers><mapper resource="com/test/dao/UserMapper.xml"></mapper>
</mappers>

进入正题：

学习Mybatis时，在resources目录下创建了com.test.dao这个包目录（自己以为成功创建了包目录）

然后在启动测试类的时候报了异常：

java.lang.ExceptionInInitializerErrorat TestDemo.getUserMapper(TestDemo.java:23)
...
Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error building SqlSession.
### The error may exist in com/test/dao/UserMapper.xml
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/test/dao/UserMapper.xmlat org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:80)at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:64)at com.test.utils.MybatisUtil.<clinit>(MybatisUtil.java:24)... 24 more
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/test/dao/UserMapper.xmlat org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:121)at org.apache.ibatis.builder.xml.XMLConfigBuilder.parse(XMLConfigBuilder.java:99)at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:78)... 26 more
Caused by: java.io.IOException: Could not find resource com/test/dao/UserMapper.xmlat org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:114)at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:100)at org.apache.ibatis.builder.xml.XMLConfigBuilder.mapperElement(XMLConfigBuilder.java:371)at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:119)... 28 morejava.lang.NullPointerException ...Process finished with exit code -1

当然，异常无非就是说我的包映射路径不对，系统找不到，我反复点开包查看，感觉没错啊？？

在打开target的classes目录时，让我产生了困惑，我的java和resources目录下都是同样的包，为什么产生了两份？？

结果发现，在resources下创建包时，不能直接将包名命名为“com.test.dao”，否则会直接将“com.test.dao”当成当前一级包名，而不是一个层级目录的包名！

后来重新在resources下创建包（需要一级一级的创建），先创建com包，然后基于com包创建test包，再基于test包创建dao包，将XxxMapper.xml文件放于dao包内，再次测试，发现运行成功，问题解决。

重新创建后的包路径：

执行成功！

D:\java\Java-8\bin\java.exe ...
update success...Process finished with exit code 0