root/tools/routingservice/branches/wrs-2.0/src/util/ObjectPool.java

/*  WRS 2.0
 *  Copyright (C) 2009 Anton Patrushev
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

package util;

import java.util.Enumeration;
import java.util.Hashtable;

public abstract class ObjectPool<T>
{
        protected String url;
        protected String user;
        protected String password;

        private long expirationTime;
        private Hashtable<T, Long> locked, unlocked;
        private int capacity;

        public ObjectPool(String url, String user, String password)
        {
                this.url = url;
                this.user = user;
                this.password = password;

                expirationTime = 60000; // 1 minute
                capacity = 10;
                locked = new Hashtable<T, Long>();
                unlocked = new Hashtable<T, Long>();

        }

        protected abstract T create();

        public abstract boolean validate(T o);

        public abstract void expire(T o);

        public synchronized T checkOut()
        {
                long now = System.currentTimeMillis();
                T t;

                if (locked.size() + unlocked.size() < capacity)
                {
                        if (unlocked.size() > 0)
                        {
                                Enumeration<T> e = unlocked.keys();

                                while (e.hasMoreElements())
                                {
                                        t = e.nextElement();

                                        if ((now - unlocked.get(t)) > expirationTime)
                                        {
                                                // object has expired
                                                unlocked.remove(t);
                                                expire(t);
                                                t = null;
                                        }
                                        else
                                        {
                                                if (validate(t))
                                                {
                                                        unlocked.remove(t);
                                                        locked.put(t, now);
                                                        return (t);
                                                }
                                                else
                                                {
                                                        // object failed validation
                                                        unlocked.remove(t);
                                                        expire(t);
                                                        t = null;
                                                }
                                        }
                                }
                        }

                        // no objects available, create a new one
                        t = create();
                        locked.put(t, now);
                        return (t);

                }
                else
                {
                        //TODO Process error
                        return null;
                }

        }

        public synchronized void checkIn(T t)
        {
                locked.remove(t);
                unlocked.put(t, System.currentTimeMillis());
        }

}