今天在用mybatis自动生成代码之后遇到了一个错误：
org.apache.ibatis.exceptions.PersistenceException :### Error building SqlSession.### The error may exist in com/erp/webservice/mapper/UsersMapper.xml### The error occurred while processing mapper_resultMap[BaseResultMap]
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.RuntimeException: Error parsing Mapper XML. Cause: java.lang.IllegalArgumentException : Result Maps collection already contains value for com.erp.webservice.inter.UsersMapper.BaseResultMap
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.erp.webservice.test.Test.<clinit>( Test.java:22)
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.lang.RuntimeException: Error parsing Mapper XML. Cause: java.lang.IllegalArgumentException : Result Maps collection already contains value for com.erp.webservice.inter.UsersMapper.BaseResultMap
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: java.lang.IllegalArgumentException : Result Maps collection already contains value for com.erp.webservice.inter.UsersMapper.BaseResultMap
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: java.lang.IllegalArgumentException: Result Maps collection already contains value for com.erp.webservice.inter.UsersMapper.BaseResultMap
at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:710)
at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:682)
at org.apache.ibatis.session.Configuration.addResultMap(Configuration.java:473)
at org.apache.ibatis.builder.MapperBuilderAssistant.addResultMap(MapperBuilderAssistant.java:204)
at org.apache.ibatis.builder.ResultMapResolver.resolve(ResultMapResolver.java:44)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElement(XMLMapperBuilder.java:277)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElement(XMLMapperBuilder.java:244)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElements(XMLMapperBuilder.java:236)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:109)
... 7 more
Exception in thread "main" java.lang.NullPointerException
at com.erp.webservice.test.Test.main( Test.java:29)
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后来发现是我运行了多次自动生成代码的程序，导致了com/erp/webservice/mapper/UsersMapper.xml的内容多出来很多，原来自动生成代码的时候生成的XML代码不是覆盖原来的，而是附加的XML的尾部的。
第一次运行自动生成代码程序：
![mybatis generator自动生成代码报The error occurred while processing mapper_resultMap[BaseResultMap]错误的解决方法](http://www.tonitech.com/wp-content/uploads/2014/03/mapper1.jpg "mybatis generator自动生成代码报The error occurred while processing mapper_resultMap[BaseResultMap]错误的解决方法")
第二次运行自动生成代码程序：
![mybatis generator自动生成代码报The error occurred while processing mapper_resultMap[BaseResultMap]错误的解决方法](http://www.tonitech.com/wp-content/uploads/2014/03/mapper2.jpg "mybatis generator自动生成代码报The error occurred while processing mapper_resultMap[BaseResultMap]错误的解决方法")
看看，XML文件明显大了很多，只要删掉原来的XML然后重新运行自动生成代码的程序即可。
或者去工作空间吧生成的东西都删除一边重新生成