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/*
 * @(#)UuidUtil.java	2011-6-16
 *
 * Copyright (c) 2011. All Rights Reserved.
 *
 */

package com.github.javaclub.jorm.common;

import java.net.InetAddress;
import java.util.UUID;

/**
 * A utility class of UUID.
 *
 * @author Gerald Chen
 * @version $Id: UuidUtil.java 193 2011-08-03 15:51:58Z [email protected] $
 */
public abstract class UuidUtil {

	/**
	 * Creates a new UUID string generated by JDK.
	 *
	 * @return UUID string
	 */
	public static String jdkUUID() {
		UUID uuid = UUID.randomUUID();
		return uuid.toString().replace("-", "");
	}
	
	/**
	 * This method is originated from hibernate framework.
	 *
	 * @return UUID string
	 */
	public static String newUUID() {
		return new StringBuffer(36)
			.append( format( getIP() ) ).append(sep)
			.append( format( getJVM() ) ).append(sep)
			.append( format( getHiTime() ) ).append(sep)
			.append( format( getLoTime() ) ).append(sep)
			.append( format( getCount() ) )
			.toString();
	}
	
	private static String format(int intval) {
		String formatted = Integer.toHexString(intval);
		StringBuffer buf = new StringBuffer("00000000");
		buf.replace( 8-formatted.length(), 8, formatted );
		return buf.toString();
	}
	
	private static String format(short shortval) {
		String formatted = Integer.toHexString(shortval);
		StringBuffer buf = new StringBuffer("0000");
		buf.replace( 4-formatted.length(), 4, formatted );
		return buf.toString();
	}
	
	/**
	 * Unique across JVMs on this machine (unless they load this class
	 * in the same quater second - very unlikely)
	 */
	private static int getJVM() {
		return JVM;
	}

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

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

	/**
	 * Unique down to millisecond
	 */
	private static short getHiTime() {
		return (short) ( System.currentTimeMillis() >>> 32 );
	}
	private static int getLoTime() {
		return (int) System.currentTimeMillis();
	}
	
	private static final int IP;
	private static String sep = "";
	
	static {
		int ipadd;
		try {
			ipadd = CommonUtil.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 static void main(String[] args) {
		for (int i = 0; i < 100; i++) {
			System.out.println(newUUID());
		}
	}
}