leasedreference.java

java pos,你可以直接编译运行,

/*
 * Copyright (c) 2000 jPOS.org.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *    "This product includes software developed by the jPOS project 
 *    (http://www.jpos.org/)". Alternately, this acknowledgment may 
 *    appear in the software itself, if and wherever such third-party 
 *    acknowledgments normally appear.
 *
 * 4. The names "jPOS" and "jPOS.org" must not be used to endorse 
 *    or promote products derived from this software without prior 
 *    written permission. For written permission, please contact 
 *    [e-mail].
 *
 * 5. Products derived from this software may not be called "jPOS",
 *    nor may "jPOS" appear in their name, without prior written
 *    permission of the jPOS project.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  
 * IN NO EVENT SHALL THE JPOS PROJECT OR ITS CONTRIBUTORS BE LIABLE FOR 
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the jPOS Project.  For more
 * information please see <http://www.jpos.org/>.
 */

package org.jpos.space;

import java.util.Timer;
import java.util.TimerTask;

/**
 * LeasedReference references an object for a limited amount of time
 * @author Alejandro Revilla
 * @version $Revision: 1.5 $ $Date: 2003/10/13 10:46:15 $
 */
public class LeasedReference extends TimerTask {
    private Object referent;
    private long expiration;

    private static Timer timer = new Timer (true);

    private LeasedReference () { }

    public LeasedReference (Object referent, long duration) {
        super ();
        this.referent = referent;
        this.expiration = System.currentTimeMillis() + duration;
        timer.schedule (this, duration);
    }
    public synchronized Object get() {
        if (isValid ())
            return this.referent;
        this.referent   = null;
        this.expiration = 0;
        super.cancel ();
        return null;
    }
    public synchronized long getExpiration () {
        return expiration;
    }
    public synchronized boolean discard () {
        if (isValid()) {
            this.referent   = null;
            this.expiration = 0;
            super.cancel ();
            return true;
        }
        return false;
    }
    public synchronized long renew (long duration) {
        if (isExpired ())
            return -1;
        return (expiration = System.currentTimeMillis() + duration);
    }
    public synchronized boolean isExpired () {
        return expiration <= System.currentTimeMillis();
    }
    public synchronized boolean isValid () {
        return expiration > System.currentTimeMillis();
    }
    public void run () {
        long duration = expiration - System.currentTimeMillis();
        if (duration < 0)
            discard ();
    }
}