com.mysql.jdbc.AbandonedConnectionCleanupThread.run(AbandonedConnectionCleanupThread.java:43)

在IDEA中部署web项目到tomcat测试后， 关闭tomcat时可能遇到以下警告信息：
com.mysql.jdbc.AbandonedConnectionCleanupThread.run(AbandonedConnectionCleanupThread.java:43)

完整信息如下：

警告 [localhost-startStop-1] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesJdbc The web application [XXX_war_exploded] 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.
警告 [localhost-startStop-1] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [XXX_war_exploded] 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:144)
com.mysql.jdbc.AbandonedConnectionCleanupThread.run(AbandonedConnectionCleanupThread.java:43)

其实意思是注册过jdbc‘驱动，但是在容器关闭时没有注销，并且是在开启了一个AbandonedConnectionCleanupThread线程中的。 所以为了内存避免泄露，就强制注销了驱动。

这是一个保护机制，并不是问题，所以可以忽略。

如果你想不打印这个警告信息，还可以这么做，写一个容器监听器，在容器销毁时，手动编码注销驱动，以下是一个简单的示例代码：

package org.byron4j;

import com.mysql.jdbc.AbandonedConnectionCleanupThread;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Enumeration;

public class MyContextListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {

    }

    // 自己写代码注销驱动
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        Enumeration<Driver> drivers = DriverManager.getDrivers();
        while (drivers.hasMoreElements()) {
            try {
                DriverManager.deregisterDriver(drivers.nextElement());
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        // 再关闭AbandonedConnectionCleanupThread线程
        try {
            AbandonedConnectionCleanupThread.shutdown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("手动注销驱动、关闭AbandonedConnectionCleanupThread线程");
    }
}

当然，不要忘了，记得在web.xml中配置一下这个监听器。