由于mybatis簡單易學，比起Hibername來，更容易上手，代碼也能自動生成。這幾天研究了下代碼自動生成的，參考：

http://0609xiaohua.iteye.com/blog/1453570

?

但是把代碼復制進來，運行了下，卻跑不起來，報以下錯誤：

Exception in thread "main" java.lang.ExceptionInInitializerError
?at com.test.Test.main(Test.java:12)
Caused by: org.apache.ibatis.exceptions.PersistenceException:?
### Error building SqlSession.
### The error may exist in com/mapper/PetMapper.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.mapper.PetMapper.BaseResultMap
?at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:8)
?at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:32)
?at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:16)
?at com.util.SessionFactory.<clinit>(SessionFactory.java:21)
?... 1 more
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.mapper.PetMapper.BaseResultMap
?at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:85)
?at org.apache.ibatis.builder.xml.XMLConfigBuilder.parse(XMLConfigBuilder.java:69)
?at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:30)
?... 3 more
Caused by: java.lang.RuntimeException: Error parsing Mapper XML. Cause: java.lang.IllegalArgumentException: Result Maps collection already contains value for com.mapper.PetMapper.BaseResultMap
?at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:97)
?at org.apache.ibatis.builder.xml.XMLMapperBuilder.parse(XMLMapperBuilder.java:73)
?at org.apache.ibatis.builder.xml.XMLConfigBuilder.mapperElement(XMLConfigBuilder.java:255)
?at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:83)
?... 5 more
Caused by: java.lang.IllegalArgumentException: Result Maps collection already contains value for com.mapper.PetMapper.BaseResultMap
?at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:578)
?at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:551)
?at org.apache.ibatis.session.Configuration.addResultMap(Configuration.java:356)
?at org.apache.ibatis.builder.MapperBuilderAssistant.addResultMap(MapperBuilderAssistant.java:138)
?at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElement(XMLMapperBuilder.java:231)
?at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElement(XMLMapperBuilder.java:201)
?at org.apache.ibatis.builder.xml.XMLMapperBuilder.resultMapElements(XMLMapperBuilder.java:196)
?at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:93)
?... 8 more

后來在CSDN上下載了個可以直接運行的eclipse 項目，再與之前的項目對比，好像也沒什么不同。最后使絕招：代碼對比工具，發現生成的PetMapper.xml多了幾百行！！！

原來是我在運行時沒有把之前已經生成的PetMapper.xml刪除掉，再次生成代碼時，又附加了上去！所以在運行代碼生成之前，要把以前已經生成的xml文件清掉，以妨出錯。

轉載于:https://www.cnblogs.com/vincent4code/p/5739772.html

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