Java如何取消驱动类的注册？

Java code

    private Driver driver = (Driver) (Class.forName(para.getJdbcDriver()).newInstance());//驱动类注册
    DriverManager.deregisterDriver(driver);//取消驱动类注册

但是在停止tomcat后还是出现：
The web application [/WebTest] registered the JDBC driver [com.microsoft.sqlserver.jdbc.SQLServerDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.

请问该怎么解决

------解决方案--------------------
貌似是Tomcat的问题

http://www.codesky.net/article/201106/148880.html