The web application [] appears to have started a thread named [thread-0]

最近在项目中，突发了一个情况，就是服务器在跑了一段时间之后，总是会莫名其妙的挂掉，初始的时候认为是服务器原因，也没有多加理会，直接重启了服务，可是当这个情况出现了两三次之后，感觉不对，还是得解决一下，这是个问题。

异常信息：

31-May-2018 09:53:48.523 WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesJdbc The web application [xw-wyyx-school] registered the JDBC driver [com.alibaba.druid.proxy.DruidDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
31-May-2018 09:53:48.524 WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesJdbc The web application [xw-wyyx-school] 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.
31-May-2018 09:53:48.530 WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [xw-wyyx-school] appears to have started a thread named [Abandoned connection cleanup thread] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
 com.mysql.jdbc.AbandonedConnectionCleanupThread.run(AbandonedConnectionCleanupThread.java:40)
31-May-2018 09:53:48.531 WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [xw-wyyx-school] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 java.util.TimerThread.mainLoop(Timer.java:552)
 java.util.TimerThread.run(Timer.java:505)
31-May-2018 09:53:48.617 INFO [main] org.apache.coyote.AbstractProtocol.stop Stopping ProtocolHandler ["http-nio-9080"]
31-May-2018 09:53:48.627 INFO [main] org.apache.coyote.AbstractProtocol.stop Stopping ProtocolHandler ["ajp-nio-9009"]
31-May-2018 09:53:48.635 INFO [main] org.apache.coyote.AbstractProtocol.destroy Destroying ProtocolHandler ["http-nio-9080"]
31-May-2018 09:53:48.636 INFO [main] org.apache.coyote.AbstractProtocol.destroy Destroying ProtocolHandler ["ajp-nio-9009"]

细看一下，原来是mysql驱动，线程回收不及时，导致tomcat守护线程报错。

解决方案：

package com.ds.utils;

import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Enumeration;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

import com.mysql.jdbc.AbandonedConnectionCleanupThread;

@WebListener
public class ContextFinalizer implements ServletContextListener {

    public void contextInitialized(ServletContextEvent sce) {
    }

    public void contextDestroyed(ServletContextEvent sce) {
        Enumeration<Driver> drivers = DriverManager.getDrivers();
        Driver d = null;
        while (drivers.hasMoreElements()) {
            try {
                d = drivers.nextElement();
                DriverManager.deregisterDriver(d);
                System.out.println(String.format("ContextFinalizer:Driver %s deregistered", d));
            } catch (SQLException ex) {
                System.out.println(String.format("ContextFinalizer:Error deregistering driver %s", d) + ":" + ex);
            }
        }
        try {
            AbandonedConnectionCleanupThread.shutdown();
        } catch (InterruptedException e) {
            System.out.println("ContextFinalizer:SEVERE problem cleaning up: " + e.getMessage());
            e.printStackTrace();
        }
    }
}