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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2012 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
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 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
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package org.glassfish.web.loader;

import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.List;

/**
 * This class is loaded by the {@link WebappClassLoader} to enable it to
 * deregister JDBC drivers forgotten by the web application. There are some
 * classloading hacks involved - see {@link WebappClassLoader#clearReferences()}
 * for details - but the short version is do not just create a new instance of
 * this class with the new keyword.
 *
 * Since this class is loaded by {@link WebappClassLoader}, it can not refer to
 * any internal Tomcat classes as that will cause the security manager to
 * complain.
 */
public class JdbcLeakPrevention {

    public List clearJdbcDriverRegistrations() throws SQLException {
        List driverNames = new ArrayList();

        /*
         * DriverManager.getDrivers() has a nasty side-effect of registering
         * drivers that are visible to this class loader but haven't yet been
         * loaded. Therefore, the first call to this method a) gets the list
         * of originally loaded drivers and b) triggers the unwanted
         * side-effect. The second call gets the complete list of drivers
         * ensuring that both original drivers and any loaded as a result of the
         * side-effects are all de-registered.
         */
        HashSet originalDrivers = new HashSet();
        Enumeration drivers = DriverManager.getDrivers();
        while (drivers.hasMoreElements()) {
            originalDrivers.add(drivers.nextElement());
        }
        drivers = DriverManager.getDrivers();
        while (drivers.hasMoreElements()) {
            Driver driver = drivers.nextElement();
            // Only unload the drivers this web app loaded
            if (driver.getClass().getClassLoader() !=
                this.getClass().getClassLoader()) {
                continue;
            }
            // Only report drivers that were originally registered. Skip any
            // that were registered as a side-effect of this code.
            if (originalDrivers.contains(driver)) {
                driverNames.add(driver.getClass().getCanonicalName());
            }
            DriverManager.deregisterDriver(driver);
        }
        return driverNames;
    }
}