mybatis执行过程中报错找不到类的问题

小菜鸟一个，写一些我遇到的问题

。

在学习mybatis的时候，按照教程的步骤一步步的操作，可是发现在最后运行的时候报错，总是启动不起来，报错是:

org.apache.ibatis.exceptions.PersistenceException: 

### Error building SqlSession.

### The error may exist in com/yihaomen/mybatis/model/User.xml

### The error occurred while processing mapper_resultMap[resultUserArticleList]

### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.RuntimeException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class . Cause: org.apache.ibatis.type.TypeException:
Could not resolve type alias 'Article'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Article
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:23)
at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:51)
at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:35)
at com.yihaomen.test.Test.<clinit>(Test.java:31)

Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.RuntimeException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class . Cause: org.apache.ibatis.type.TypeException:
Could not resolve type alias 'Article'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Article
at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:107)
at org.apache.ibatis.builder.xml.XMLConfigBuilder.parse(XMLConfigBuilder.java:89)
at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:49)
... 2 more

Caused by: java.lang.RuntimeException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class . Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Article'.  Cause: java.lang.ClassNotFoundException:
Cannot find class: Article
at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:113)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.parse(XMLMapperBuilder.java:88)
at org.apache.ibatis.builder.xml.XMLConfigBuilder.mapperElement(XMLConfigBuilder.java:325)
at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:105)
... 4 more

Caused by: org.apache.ibatis.builder.BuilderException: Error resolving class . Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Article'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Article
at org.apache.ibatis.builder.BaseBuilder.resolveClass(BaseBuilder.java:94)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElement(XMLMapperBuilder.java:257)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElement(XMLMapperBuilder.java:244)
at org.apache.ibatis.builder.xml.XMLMapperBuilde
4000
r.resultMapElements(XMLMapperBuilder.java:236)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:109)
... 7 more

Caused by: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Article'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Article
at org.apache.ibatis.type.TypeAliasRegistry.resolveAlias(TypeAliasRegistry.java:113)
at org.apache.ibatis.builder.BaseBuilder.resolveAlias(BaseBuilder.java:121)
at org.apache.ibatis.builder.BaseBuilder.resolveClass(BaseBuilder.java:92)
... 11 more

Caused by: java.lang.ClassNotFoundException: Cannot find class: Article
at org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:188)
at org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:87)
at org.apache.ibatis.io.Resources.classForName(Resources.java:254)
at org.apache.ibatis.type.TypeAliasRegistry.resolveAlias(TypeAliasRegistry.java:109)
... 13 more

Exception in thread "main" java.lang.NullPointerException
at com.yihaomen.test.Test.main(Test.java:111)

一直找啊找啊找都没找到问题在哪里，因为是菜鸟啊，什么都不懂，最后才发现原来是作者忘记要在configuration.xml中添加一行代码，就是

<typeAliases> 

        <typeAlias alias="User" type="com.model.User"/>

        <typeAlias alias="Article" type="com.model.Article"/>  

  </typeAliases> 

中间绿色那一条，所以系统才找不到Article。