背景，mybatis查询的时候直接取的sqlsession,没有包装成SqlSessionTemplate,没有走spring提供的代理。
然后我写的获取sqlsession的代码没有考虑到并发的情况，导致sqlsession建的太多
并发大了之后，查询报错
org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: java.lang.ClassCastException: org.apache.ibatis.executor.ExecutionPlaceholder cannot be cast to java.util.List
### The error may exist in class path resource [mybatis/ConVideoInfoMapper.xml]
### The error may involve com.letv.mms.core.dao.IConVideoInfoDao.selectById
### The error occurred while executing a query
### Cause: java.lang.ClassCastException: org.apache.ibatis.executor.ExecutionPlaceholder cannot be cast to java.util.List
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:23) ~[mybatis-3.1.1.jar:3.1.1]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:104) ~[mybatis-3.1.1.jar:3.1.1]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:95) ~[mybatis-3.1.1.jar:3.1.1]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:59) ~[mybatis-3.1.1.jar:3.1.1]
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:95) ~[mybatis-3.1.1.jar:3.1.1]
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:40) ~[mybatis-3.1.1.jar:3.1.1]
解决方法，交给spring来管理mybatis，使用sqlsessiontemplate。