代碼如下：

這是不可以的，會報錯：

2016-08-18 11:36:00,267 [main] ERROR [org.mybatis.spring.mapper.MapperFactoryBean] - Error while adding the mapper 'interface com.unix21.mapper.UserMapper' to configuration.java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.unix21.mapper.UserMapper.findByIdat org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:837)at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:809)at org.apache.ibatis.session.Configuration.addMappedStatement(Configuration.java:633)at org.apache.ibatis.builder.MapperBuilderAssistant.addMappedStatement(MapperBuilderAssistant.java:302)at org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parseStatement(MapperAnnotationBuilder.java:325)at org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parse(MapperAnnotationBuilder.java:130)at org.apache.ibatis.binding.MapperRegistry.addMapper(MapperRegistry.java:72)at org.apache.ibatis.session.Configuration.addMapper(Configuration.java:706)at org.mybatis.spring.mapper.MapperFactoryBean.checkDaoConfig(MapperFactoryBean.java:81)

class MapperFactoryBean在mybatis-spring.jar

原因一步步調試出來

org.mybatis.spring.mapper.MapperFactoryBean.checkDaoConfig

class Configuration在mybatis.jar

org.apache.ibatis.session.Configuration.addMapper

org.apache.ibatis.binding.MapperRegistry.addMapper

knownMappers

MapperProxyFactory

knownMappers.put

org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parse

Method[] methods = type.getMethods();

org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parseStatement

resultMapId = parseResultMap(method);

parseResultMap

applyResultMap

applyResults

applyResultMap

addResultMap

回到applyResultMap

回到parseResultMap

回到parseStatement

org.apache.ibatis.builder.MapperBuilderAssistant.addMappedStatement

statementBuilder.parameterMap

org.apache.ibatis.mapping.MappedStatement.parameterMap

回到addMappedStatement

org.apache.ibatis.mapping.MappedStatement.Builder.build

回到addMappedStatement

重點來了

org.apache.ibatis.session.Configuration.addMappedStatement

mappedStatements定義

StrictMap定義繼承自HashMap重寫了put

多了一行判斷

if (containsKey(key))?

第一次當然是containsKey(key)=false

返回addMappedStatement，mappedStatements添加完成

一直退到parse

第二次for循環methods

一直下一步...到了第二次mappedStatements.put

containsKey(key)==true產生異常

總結

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