/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


package org.apache.catalina.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;
import java.util.Set;

This class is loaded by WebappClassLoaderBase to enable it to deregister JDBC drivers forgotten by the web application. There are some classloading hacks involved - see WebappClassLoaderBase.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 WebappClassLoaderBase, it cannot refer to any internal Tomcat classes as that will cause the security manager to complain. /**
 * This class is loaded by {@link WebappClassLoaderBase} to enable it to
 * deregister JDBC drivers forgotten by the web application. There are some
 * classloading hacks involved - see
 * {@link WebappClassLoaderBase#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 WebappClassLoaderBase}, it cannot refer
 * to any internal Tomcat classes as that will cause the security manager to
 * complain.
 */
public class JdbcLeakPrevention {

    public List<String> clearJdbcDriverRegistrations() throws SQLException {
        List<String> 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.
         */
        Set<Driver> originalDrivers = new HashSet<>();
        Enumeration<Driver> 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;
    }
}