POS Oracle drivers refusing to unload, causing memory leaks, and killing the god damn PermGen space.

OjdbcDriverListener.java

package com.jrfom.fuck.oracle;

import java.lang.management.ManagementFactory;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.Hashtable;

import javax.management.MBeanServer;
import javax.management.ObjectName;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import oracle.jdbc.OracleDriver;
import oracle.ucp.UniversalConnectionPoolException;
import oracle.ucp.admin.UniversalConnectionPoolManager;
import oracle.ucp.admin.UniversalConnectionPoolManagerImpl;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>The Oracle driver is a piece of shit. This will keep us from leaking memory
 * across re-deployments.</p>
 *
 * <p>Taken from http://stackoverflow.com/a/15816247</p>
 * <p>With support from https://blogs.reucon.com/srt/classloader-leaks-by-oracle-9056/</p>
 */
public class OjdbcDriverListener implements ServletContextListener {
  private static final Logger log = LoggerFactory.getLogger(OjdbcDriverListener.class);

  private Driver driver;

  @Override
  public void contextInitialized(ServletContextEvent sce) {
    this.driver = new OracleDriver();
    boolean skipRegistration = false;
    Enumeration<Driver> drivers = DriverManager.getDrivers();

    while (drivers.hasMoreElements()) {
      Driver driver = drivers.nextElement();
      if (driver instanceof OracleDriver) {
        OracleDriver alreadyRegistered = (OracleDriver) driver;
        if (alreadyRegistered.getClass() == this.driver.getClass()) {
          skipRegistration = true;
          this.driver = alreadyRegistered;
          break;
        }
      }
    }

    try {
      if (!skipRegistration) {
        DriverManager.registerDriver(this.driver);
        log.info(
          "Registered JDBC driver: `{} v{}.{}`",
          this.driver,
          this.driver.getMajorVersion(),
          this.driver.getMinorVersion()
        );
      }
    } catch (SQLException e) {
      log.error("Could not register Oracle driver: `{}`", e.getMessage());
      log.debug(e.toString());
      throw new RuntimeException(e);
    }
  }

  @Override
  public void contextDestroyed(ServletContextEvent sce) {
    if (this.driver != null) {
      try {
        log.info("Killing the Oracle universal connection pool");
        UniversalConnectionPoolManager mgr = UniversalConnectionPoolManagerImpl.getUniversalConnectionPoolManager();
        mgr.setJmxEnabled(false);
        mgr.destroyConnectionPool("the_name_of_your_connection_pool");

        log.info("Killing some bullshit MBeans");
        this.killMBeans();

        DriverManager.deregisterDriver(this.driver);
        log.info("Deregistered JDBC driver: `{}`", this.driver);
      } catch (SQLException e) {
        log.error("Could not deregister driver: `{}`", e.getMessage());
        log.debug(e.toString());
      } catch (UniversalConnectionPoolException e) {
        log.error("Could not get connection pool manager: `{}`", e.getMessage());
        log.debug(e.toString());
      }

      this.driver = null;
    } else {
      log.info("No JDBC driver to deregister");
    }
  }

  private void killMBeans() {
    final ClassLoader cl = Thread.currentThread().getContextClassLoader();

    try {
      final MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();

      for (ObjectName mbean : mbs.queryNames(null, null)) {
        final Hashtable<String, String> keys = new Hashtable<>();
        final String mbeanName = mbean.getCanonicalName();
        final Hashtable<String, String> properties = mbean.getKeyPropertyList();

        /*log.debug("Bean => {}", mbeanName);
        for (String k : properties.keySet()) {
          log.debug("[{} : {}]", k, properties.get(k));
        }*/

        if (mbeanName.startsWith("oracle.ucp.admin") ||
            mbeanName.startsWith("com.oracle.jdbc"))
        {
          log.debug("Killing MBean: `{}`", mbeanName);
          keys.put("name", properties.get("name"));
          if (properties.containsKey("type")) {
            keys.put("type", properties.get("type"));
          }

          ObjectName objectName = new ObjectName(mbeanName.split(":")[0], keys);
          mbs.unregisterMBean(objectName);
        }
      }
    } catch (Exception e) {
      log.error("Could not deregister MBean: `{}`", e.getMessage());
      log.debug(e.toString());
    }
  }
}