报错场景：spring boot+mybatis，线程池执行批量任务。springboot正常启动后，定时任务中数据库查询报错。报错信息如下：
1 Caused by: org.apache.ibatis.exceptions.PersistenceException: 2 ### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; 3 nested exception is com.alibaba.druid.pool.DataSourceClosedException: dataSource already closed at Wed Jun 30 17:31:57 GMT+08:00 2021 4 ### The error may exist in URL [jar:file:/home/xxx/xxx/xxx-1.0.jar!/BOOT-INF/lib/common-1.0.jar!/mapper/basedata_mapper/xxxMapper.xml] 5 ### The error may involve com.xxx.common.basedata.dao.xxxTaskDao.getListByCode 6 ### The error occurred while executing a query 7 ### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is com.alibaba.druid.pool.DataSourceClosedException: dataSource already closed at Wed Jun 30 17:31:57 GMT+08:00 2021 8 at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30) 9 at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150) 10 at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141) 11 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 12 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) 13 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 14 at java.lang.reflect.Method.invoke(Method.java:498) 15 at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433) 16 ... 15 common frames omitted
解决：
多线程批量处理的时候只需要在service方法上加上@transactional(rollbackFor = Exception.class)就行了,mybatis就不会每次执行完sql后closing sql session了
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参考：
https://github.com/alibaba/druid/issues/1625