idgenerator.java

A Java web application, based on Struts and Hibernate, that serves as an online running log. Users m

/* @LICENSE_COPYRIGHT@ */
package net.sf.irunninglog.util;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Class used to generate pseudo-unique id values.  This class can be used to
 * generate values that are unique within the currently running JVM.  Values
 * may be repeated after a server restart, etc. so these values should only be
 * used to identify short-lived data.
 *
 * @author <a href="mailto:[e-mail]">Allan Lewis</a>
 * @version $Revision: 1.1.1.1 $ $Date: 2005/06/23 01:49:03 $
 * @since iRunningLog 1.0
 */
public final class IdGenerator {

    /** <code>Log</code> instance for this class. */
    private static final Log LOG = LogFactory.getLog(IdGenerator.class);
    /** Singleton instance. */
    private static final IdGenerator INSTANCE;

    /** The last id that was gegnerated. */
    private long mLastId;

    static {
        INSTANCE = new IdGenerator();
    }

    /** Utility class - protect the default constructor. */
    private IdGenerator() {
        super();
        mLastId = 0;

        if (LOG.isDebugEnabled()) {
            LOG.debug("Id generator has been successfully initialized");
        }
    }

    /**
     * Generate and return a new identifier.  This method is guananteed to
     * return a value that is unique <strong>within the life span of the
     * currently </strong> running server.  Values returned from this method
     * are <strong>NOT</strong> guaranteed to be unique beyond that time frame.
     *
     * @return The generated identifier
     */
    public static synchronized long generateId() {
        long id = INSTANCE.mLastId;

        if (LOG.isDebugEnabled()) {
            LOG.debug("generateId: Generated an id of '" + id + "'");
        }

        INSTANCE.mLastId += 1;

        return id;
    }

}