参见 这个答案.似乎 MySQL 驱动程序应该在应用程序之间共享的 {$TOMCAT]/lib 中.检查您是否没有将它包含在每个应用程序中.至少它对我有用，我已经能够删除警告.

See this answer. It seems that MySQL driver should be in {$TOMCAT]/lib shared between applications. Check that you are not including it with each application. At least it worked for me and I have been able to remove the warning.

如果您使用 Maven，请将依赖项标记为已提供.

If you are using Maven mark the dependency as provided.

更新:
根本原因是 Tomcat 在对驱动程序进行垃圾回收方面存在问题，因为它注册在多个应用程序通用的单例中.关闭一个应用程序不允许 Tomcat 释放驱动程序.请参阅此答案.