【mybatis】使用mybatis框架中踩过的坑

好久没来记录一下自己的学习情况，最近都在学框架，今天来记录一下关于mybatis框架的学习过程中碰过的一些问题：

以下内容可能稍微有点凌乱，因为是把之前遇到过的错误或异常都集中一起了，不过我已经把问题原因or解决方法加粗了，方便查看，少部分问题是暂时未知原因，如果哪位大神知道原因欢迎留言，我后面如果知道了原因也会对应更新！^ ^

org.apache.ibatis.exceptions.PersistenceException:
### Error building SqlSession.
### The error may exist in SQL Mapper Configuration
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.datasource.DataSourceException: Unknown DataSource property: drvier

at 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 App_1_type.findById(App_1_type.java:21)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)

Class not found: "App_1_type"Empty test suite.

出现这个错误的时候，打开maven面板，看看里面有没有这个模块的信息（我这次在maven面板找不到目前这个项目）所以在maven面板把当前模块添加进去即可

at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.datasource.DataSourceException: Unknown DataSource property: drvier
at 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)
... 24 more
Caused by: org.apache.ibatis.datasource.DataSourceException: Unknown DataSource property: drvier
at org.apache.ibatis.datasource.unpooled.UnpooledDataSourceFactory.setProperties(UnpooledDataSourceFactory.java:55)
at org.apache.ibatis.builder.xml.XMLConfigBuilder.dataSourceElement(XMLConfigBuilder.java:326)
at org.apache.ibatis.builder.xml.XMLConfigBuilder.environmentsElement(XMLConfigBuilder.java:280)
at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:116)
... 26 more
暂不清楚，只是把前一个项目的driver配置复制过来就OK，然后还原会原来的driver配置也OK了

org.apache.ibatis.exceptions.PersistenceException:
### Error updating database. Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'userId111' in 'class com.itheima.entity.User'
### The error may involve com.itheima.dao.IUserDao.delete-Inline
### The error occurred while setting parameters
### SQL: DELETE FROM user WHERE id = ?;
### Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'userId111' in 'class com.itheima.entity.User'

at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:200)
at org.apache.ibatis.session.defaults.DefaultSqlSession.delete(DefaultSqlSession.java:213)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:67)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
at com.sun.proxy.$Proxy5.delete(Unknown Source)
at App_1_type.delete(App_1_type.java:167)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'userId111' in 'class com.itheima.entity.User'
at org.apache.ibatis.reflection.Reflector.getGetInvoker(Reflector.java:419)
at org.apache.ibatis.reflection.MetaClass.getGetInvoker(MetaClass.java:164)
at org.apache.ibatis.reflection.wrapper.BeanWrapper.getBeanProperty(BeanWrapper.java:162)
at org.apache.ibatis.reflection.wrapper.BeanWrapper.get(BeanWrapper.java:49)
at org.apache.ibatis.reflection.MetaObject.getValue(MetaObject.java:122)
at org.apache.ibatis.scripting.defaults.DefaultParameterHandler.setParameters(DefaultParameterHandler.java:79)
at org.apache.ibatis.executor.statement.PreparedStatementHandler.parameterize(PreparedStatementHandler.java:93)
at org.apache.ibatis.executor.statement.RoutingStatementHandler.parameterize(RoutingStatementHandler.java:64)
at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:86)
at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:49)
at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117)
at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:76)
at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:198)
... 27 more
这个异常是因为我接口的方法传入了对象作为参数，但是在IUserDao.xml里配置的#{}没有使用对象属性名字。
解决：把#{}里的内容改为对象的属性名，或者把接口方法的传入参数改为int id

Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Parsing error was found in mapping #{}. Check syntax #{property|(expression), var1=value1, var2=value2, ...}
配置文件写错！

异常：
org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: org.apache.ibatis.reflection.ReflectionException: Could not set property 'id' of 'class com.itheima.entity.Account' with value '41' Cause: org.apache.ibatis.reflection.ReflectionException: There is no setter for property named 'id' in 'class com.itheima.entity.Account'
### The error may exist in com/itheima/dao/IUserDao.xml
### The error may involve com.itheima.dao.IUserDao.findAllUser
### The error occurred while handling results
### SQL: select * from user u left join account a on u.id=a.UID
### Cause: org.apache.ibatis.reflection.ReflectionException: Could not set property 'id' of 'class com.itheima.entity.Account' with value '41' Cause: org.apache.ibatis.reflection.ReflectionException: There is no setter for property named 'id' in 'class com.itheima.entity.Account'

java.io.IOException: Could not find resource SqlMapConfig.xml

at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:114)
at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:100)
at App.init(App.java:31)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

这个应该是idea的问题，重启之后可以找到文件

java.lang.NullPointerException
at App.findAccounts(App.java:52)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

原因：是因为accountDao接口没有生成代理对象

org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: org.apache.ibatis.executor.ExecutorException: No constructor found in com.itheima.entity.User matching [java.lang.Integer, java.lang.String, java.sql.Timestamp, java.lang.String, java.lang.String, java.lang.Integer, java.lang.String, java.lang.String]
### The error may exist in com/itheima/dao/IUserDao.xml
### The error may involve com.itheima.dao.IUserDao.findAllUser
### The error occurred while handling results
### SQL: SELECT u.*,r.ID role_id,r.ROLE_NAME ,r.ROLE_DESC FROM user u INNER JOIN user_role ur INNER JOIN role r on u.id = ur.UID AND ur.RID = r.ID
### Cause: org.apache.ibatis.executor.ExecutorException: No constructor found in com.itheima.entity.User matching [java.lang.Integer, java.lang.String, java.sql.Timestamp, java.lang.String, java.lang.String, java.lang.Integer, java.lang.String, java.lang.String]

原因：就是因为实体类User里面的有参构造器覆盖了默认的无参构造器，所以无法封装。
解决：添加无参构造器，或者把所有有参构造器去掉。
后面框架一般都用无参构造器来封装，所以实体类可以不用给构造器，如果要给构造器一定要给一个无参的。

log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
重启idea后正常（原因不明）

org.apache.ibatis.binding.BindingException: Type interface com.itheima.dao.IRoleDao is not known to the MapperRegistry.

at org.apache.ibatis.binding.MapperRegistry.getMapper(MapperRegistry.java:47)
at org.apache.ibatis.session.Configuration.getMapper(Configuration.java:745)
at org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper(DefaultSqlSession.java:292)
at App.init(App.java:35)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
原因：没有在SqlMapConfig.xml中配置<mapper>指定dao的映射文件位置。导致找不到对应的接口

org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.davina.dao.IUserDao.findUsers
配置文件路径命名要用/ 否则目录层级不对，就报这个错误，因为找不到IXxxxDao.xml

Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'user'. Cause: java.lang.ClassNotFoundException: Cannot find class: user
因为没有用别名，但是<resultMap id="userResultMap" type="com.davina.entity.User">的type用了user。如果没有取别名就应该用包全名

Caused by: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'username' in 'class com.davina.entity
原因配置IUserDao.xml的时候在配置这个条件的时候 AND username = #{user.username} 漏了user.所以提示找不到username

当程序报出找不到SqlMapConfig.xml文件的时候，可以去maven面板检查该模块是否存在，不存在则添加，然后再来测试

Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'account'. Cause: java.lang.ClassNotFoundException: Cannot find class: account
没有起别名的时候IxxxDao.xml文件中配置类型相关的属性时，要写类全名，否则找不到

异常
Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.itheima.dao.IAccountDao.
原因在延迟加载配置中 select属性没有给出引用的“包名.方法”信息

<script> select * from user where 1=1 <if test="username != null and username != ''">and username=#{username}</if></script>

异常
org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.itheima.dao.IUserDao.findById

at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:225)
at org.apache.ibatis.binding.MapperMethod.<init>(MapperMethod.java:48)
at org.apache.ibatis.binding.MapperProxy.cachedMapperMethod(MapperProxy.java:65)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:58)
at com.sun.proxy.$Proxy11.findById(Unknown Source)
at App.findById(App.java:84)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

这个原因是我拷贝了一个项目练习注解开发的时候删掉了resources文件夹下的dao映射文件，所以找不到接口。。。

Caused by: java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.itheima.dao.IUserDao.findById

这个异常原因就是：xml和注解都映射了同一个方法！去掉其中一个映射即可

Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.itheima.dao.IUserDao.findUserById
这个异常是因为改用注解开发一对一延时加载后，target文件夹下仍然有映射文件，所以要clean一下，再运行。

注意：注解开发中，SqlMapConfig.xml也要配置mapper否则会报org.apache.ibatis.binding.BindingException: Type interface com.itheima.dao.IUserDao is not known to the MapperRegistry.
MapperRegistry.相关的错误基本都是跟SqlMapConfig.xml中的mapper配置有关

Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/itheima/dao/IUserDao.xml
这是因为SqlMapConfig.xml中的mappers配置里仍然用了mapper来配置映射文件，而注解开发中本来就不需要映射文件，所以报映射文件找不到
所以应该把主配置文件SqlMapConfig.xml里mappers标签改为用package配置方式（这个配置方式适用于xml和注解开发，推荐使用）

### The error may exist in com/davina/dao/IAccountDao.xml
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: SELECT * FROM account a INNER JOIN user u ON a.id = u.id;
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'a.id' in 'on clause'
这个错误实际上不是在IAccountDao.xml，最后两句说了原因是SQL找不到id字段，所以要检查哪里用到这个SQL！
然后在IAccountDao.xml发现了这个SQL

刚刚出现一个奇葩问题，运行一对多延时加载测试的时候，没有进行延时加载，输出的结果为：
用户名：老王
账户名：null
用户名：小二王
账户名：null
用户名：哈哈
账户名：null
用户名：传智播客
账户名：null
用户名：呵呵
账户名：null
用户名：小马宝莉
账户名：null
即没有延时效果，并且没有查到账户信息，但是如果断点调试又可以看到账户信息
经检查发现：在User实体类中：
有成员List<Account> accounts;
而该成员的get方法为getAccouts()即不是标准的方法，因为之前发现单词拼错，改了成员变量名，但是get/set方法对应的方法名没改、
更改后运行正常