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

Question

I am getting this message when I run my web application. It runs fine but I get this message during shutdown.

SEVERE: A web application registered the

Answer 1

To prevent this memory leak, simply deregister the driver on context shutdown.

pom.xml

    4.0.0

    com.mywebsite
    emusicstore
    1.0-SNAPSHOT

    
        
            
                org.apache.maven.plugins
                maven-compiler-plugin
                3.7.0
                
                    1.9
                    1.9
                
            
        
    

    
        

        
            org.hibernate
            hibernate-core
            4.0.1.Final
        

        
            org.hibernate.javax.persistence
            hibernate-jpa-2.0-api
            1.0.1.Final
        

        
        
            mysql
            mysql-connector-java
            8.0.11
        

        
        
            javax.servlet
            servlet-api
            2.5
            provided
        
    

MyWebAppContextListener.java

package com.emusicstore.utils;

import com.mysql.cj.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 MyWebAppContextListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("************** Starting up! **************");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("************** Shutting down! **************");
        System.out.println("Destroying Context...");
        System.out.println("Calling MySQL AbandonedConnectionCleanupThread checkedShutdown");
        AbandonedConnectionCleanupThread.checkedShutdown();

        ClassLoader cl = Thread.currentThread().getContextClassLoader();

        Enumeration drivers = DriverManager.getDrivers();
        while (drivers.hasMoreElements()) {
            Driver driver = drivers.nextElement();

            if (driver.getClass().getClassLoader() == cl) {
                try {
                    System.out.println("Deregistering JDBC driver {}");
                    DriverManager.deregisterDriver(driver);

                } catch (SQLException ex) {
                    System.out.println("Error deregistering JDBC driver {}");
                    ex.printStackTrace();
                }
            } else {
                System.out.println("Not deregistering JDBC driver {} as it does not belong to this webapp's ClassLoader");
            }
        }
    }

}

web.xml

    
        com.emusicstore.utils.MyWebAppContextListener
    

Source that inspired me for this bug fix.