To prevent a memory leak, the JDBC Driver has been forcibly unregistered

在Java开发中遇到的问题，一下是错误提示信息：
七月 10, 2015 6:21:56 下午 org.apache.catalina.core.StandardContext startInternal
严重: One or more listeners failed to start. Full details will be found in the appropriate container log file
七月 10, 2015 6:21:56 下午 org.apache.catalina.core.StandardContext startInternal
严重: Context [] startup failed due to previous errors
七月 10, 2015 6:21:56 下午 org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
严重: The web application [] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
[2015-07-10 06:21:56,141] Artifact yiilnli-backend:war exploded: Error during artifact deployment. See server log for details.

网上搜索的相关问题的解释。

org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
严重: A web application registered the JBDC driver [oracle.jdbc.driver.OracleDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.

给出的答案是，类似于：好像是说JDBC驱动没有注册？如何解决？

自己分析问题，找出的答案是由于自己定义的字段和继承的基类中的字段相互冲突了，这边字段重写，导致的错误。
以下截图：

基类的截图：

解决方法，删除自己后来定义的字段，编译就没错误了。