Exception in thread "main" org.hibernate.exception.GenericJDBCException: Cannot open connection

hibernate连接mysql数据库时运行代码，出现这个错误
因为报错是cannot open connection，开始一直以为是数据库连接的问题

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.annotations.Version).
log4j:WARN Please initialize the log4j system properly.
Exception in thread "main" org.hibernate.exception.GenericJDBCException: Cannot open connection
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Caused by: java.sql.SQLException: Unknown system variable 'tx_isolation'
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后来发现出错原因是没有加日志的属性文件log4j.properties，加上属性文件之后，程序就可以运行了