MyBatis - Mapped Statements collection already contains value for

Question

I had the following error messages thrown when registering the mapper classes on my server startup,

[artifact:mvn] 2016-05-07 11:39:21,708 [ERROR] org.mybatis.spring.mapper.MapperFactoryBean - Error while adding the mapper 'interface com.sample.mappers.UserMapper' to configuration.
[artifact:mvn] java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.sample.mappers.UserMapper.getAllUsers
[artifact:mvn]  at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:802)
[artifact:mvn]  at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:774)
[artifact:mvn]  at org.apache.ibatis.session.Configuration.addMappedStatement(Configuration.java:598)
[artifact:mvn]  at org.apache.ibatis.builder.MapperBuilderAssistant.addMappedStatement(MapperBuilderAssistant.java:300)
[artifact:mvn]  at org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parseStatement(MapperAnnotationBuilder.java:313)
[artifact:mvn]  at org.apache.ibatis.builder.annotation.MapperAnnotationBuilder.parse(MapperAnnotationBuilder.java:128)
[artifact:mvn]  at org.apache.ibatis.binding.MapperRegistry.addMapper(MapperRegistry.java:72)
[artifact:mvn]  at org.apache.ibatis.session.Configuration.addMapper(Configuration.java:671)
[artifact:mvn]  at org.mybatis.spring.mapper.MapperFactoryBean.checkDaoConfig(MapperFactoryBean.java:81)
[artifact:mvn]  at org.springframework.dao.support.DaoSupport.afterPropertiesSet(DaoSupport.java:44)

I used annotations for my mapper interfaces and there's no xml configuration.

Below is my UserMapper interface,

public interface UserMapper {

  @Select("SELECT  * FROM customer")
  List<User> getAllUsers();

  @Select("SELECT * FROM customer where userId = #{userId} ")
  List<User> getAllUsers(Long userId);

}

Answer 1

I found out the cause of the error message. If you have the same method name, then mybatis throws the Mapped Statements collection already contains value error message. So the solution is to have different method names for different mapper statements even if the method signatures are different.

So In my mapper interface the method names second getAllUsers() name should be getUserById();. The same error is thrown if you have the same method name in any of the mapper.xml files. So it is mandatory to have unique method names or mapper namespace for different sql statements for mybatis to map this at runtime.