AbstractUUIDGenerator.java

/*
 * @(#)AbstractUUIDGenerator.java 2012-8-1 下午10:00:00
 *
 * Copyright (c) 2011-2012 Makersoft.org all rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 *
 */
package org.makersoft.shards.id.uuid;

import java.net.InetAddress;

import org.makersoft.shards.utils.BytesHelper;

/**
 * The base class for identifier generators that use a UUID algorithm. This
 * class implements the algorithm, subclasses define the identifier format.
 * 
 * @see UUIDHexGenerator
 * @author Gavin King
 */

public abstract class AbstractUUIDGenerator {
	private static final int IP;
	static {
		int ipadd;
		try {
			ipadd = BytesHelper.toInt(InetAddress.getLocalHost().getAddress());
		} catch (Exception e) {
			ipadd = 0;
		}
		IP = ipadd;
	}
	private static short counter = (short) 0;
	private static final int JVM = (int) (System.currentTimeMillis() >>> 8);

	public AbstractUUIDGenerator() {
	}

	/**
	 * Unique across JVMs on this machine (unless they load this class in the
	 * same quater second - very unlikely)
	 */
	protected int getJVM() {
		return JVM;
	}

	/**
	 * Unique in a millisecond for this JVM instance (unless there are >
	 * Short.MAX_VALUE instances created in a millisecond)
	 */
	protected short getCount() {
		synchronized (AbstractUUIDGenerator.class) {
			if (counter < 0)
				counter = 0;
			return counter++;
		}
	}

	/**
	 * Unique in a local network
	 */
	protected int getIP() {
		return IP;
	}

	/**
	 * Unique down to millisecond
	 */
	protected short getHiTime() {
		return (short) (System.currentTimeMillis() >>> 32);
	}

	protected int getLoTime() {
		return (int) System.currentTimeMillis();
	}

}