The web application registered the 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.

最近使用了最新版的tomcat9,使用jdbc链接mysql数据库。关闭tomcat过程中出现警告

13-Sep-2017 22:22:54.369 WARNING [main] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesJdbc The web application [license] 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.

时间有限没有去追源码，网上的说法：

tomcat6最新版本引入内存溢出检测阻止机制，检测到jdbc在tomcat运行时进行注册，但是当tomcat停止时没有解除注册。

原因是在tomcat停止之前没注销驱动。

网上有的方式是重写org.apache.commons.dbcp.BasicDataSource,这个不推荐。既然是容器级别的事件，那就从事件入手。

@WebListener
public class AppContextListener implements ServletContextListener{

    public void contextDestroyed(ServletContextEvent event)  {
         try{
             while(DriverManager.getDrivers().hasMoreElements()){
                 DriverManager.deregisterDriver(DriverManager.getDrivers().nextElement());
            }
         }catch(Exception e){
             e.printStackTrace();
         }
    }

    public void contextInitialized(ServletContextEvent event)  { 
          ServletContext context = event.getServletContext();
          String rootPath = context.getRealPath("/");
          System.setProperty("rootPath", rootPath);
          
          //logger.info("global setting,rootPath:{}",rootPath);
           //logger.info("deployed on architecture:{},operation System:{},version:{}",
            //       System.getProperty("os.arch"), System.getProperty("os.name"),
                //   System.getProperty("os.version"));           
           //logger.info("app startup completed....");
    }
}

Tomcat在停止web应用的时候会调用contextDestroyed方法，加入你的项目,即可在tomcat关闭时注销已经注册的JDBC驱动。

以上代码适用于servlet3.0 web容器，servlet 2.5容器需要在web.xml添加配置文件。

servlet容器2.5用法

public class AppContextListener implements ServletContextListener{

    public void contextDestroyed(ServletContextEvent event)  {
         try{
             while(DriverManager.getDrivers().hasMoreElements()){
                 DriverManager.deregisterDriver(DriverManager.getDrivers().nextElement());
            }
         }catch(Exception e){
             e.printStackTrace();
         }
    }

    public void contextInitialized(ServletContextEvent event)  { 
          ServletContext context = event.getServletContext();
          String rootPath = context.getRealPath("/");
          System.setProperty("rootPath", rootPath);
          
          //logger.info("global setting,rootPath:{}",rootPath);
           //logger.info("deployed on architecture:{},operation System:{},version:{}",
            //       System.getProperty("os.arch"), System.getProperty("os.name"),
                //   System.getProperty("os.version"));           
           //logger.info("app startup completed....");
    }
}

web.xml

<web-app>
  <listener>
        <listener-class>com.xxxx.init.AppContextListener</listener-class>
    </listener>
</web-app>

至此，问题解决。