ID generator : UUID « Development « Java Tutorial

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/*
    GNU LESSER GENERAL PUBLIC LICENSE
    Copyright (C) 2006 The Lobo Project

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library 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
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Contact info: lobochief@users.sourceforge.net
*/
/*
 * Created on Jun 7, 2005
 */

import java.util.*;
import java.util.logging.*;
import java.security.*;
import java.math.*;
import java.net.InetAddress;

/**
 * @author J. H. S.
 */
public class ID {
  private static final Random RANDOM1;
  private static final Random RANDOM2;
  private static final Random RANDOM3;
  private static final long globalProcessID;
    private static final Logger logger = Logger.getLogger(ID.class.getName());

    static {
    long time = System.currentTimeMillis();
    long nanoTime = System.nanoTime();
    long freeMemory = Runtime.getRuntime().freeMemory();
    long addressHashCode;
    try {
      InetAddress inetAddress;
      inetAddress = InetAddress.getLocalHost();
      addressHashCode = inetAddress.getHostName().hashCode() ^ inetAddress.getHostAddress().hashCode();
    } catch(Exception err) {
      logger.log(Level.WARNING, "Unable to get local host information.", err);
      addressHashCode = ID.class.hashCode();
    }   
    globalProcessID = time ^ nanoTime ^ freeMemory ^ addressHashCode;   
    RANDOM1 = new Random(time);
    RANDOM2 = new Random(nanoTime);
    RANDOM3 = new Random(addressHashCode ^ freeMemory);
  }
  
  private ID() {
  }
  
  public static long generateLong() {
    return Math.abs(RANDOM1.nextLong() ^ RANDOM2.nextLong() ^ RANDOM3.nextLong());
  }
  
  public static int generateInt() {
    return (int) generateLong();
  }
  
  public static byte[] getMD5Bytes(String content) {
        try {
            MessageDigest digest = MessageDigest.getInstance("MD5");
            return digest.digest(content.getBytes("UTF-8"));
        } catch (NoSuchAlgorithmException e) {
          throw new IllegalStateException(e);
    } catch(java.io.UnsupportedEncodingException uee) {
      throw new IllegalStateException(uee);
    }
  }

  public static String getHexString(byte[] bytes) {
    // This method cannot change even if it's wrong.
    BigInteger bigInteger = BigInteger.ZERO;
    int shift = 0;
    for(int i = bytes.length; --i >= 0;) {
      BigInteger contrib = BigInteger.valueOf(bytes[i] & 0xFF);
      contrib = contrib.shiftLeft(shift);
      bigInteger = bigInteger.add(contrib);
      shift += 8;
    }
    return bigInteger.toString(16).toUpperCase();
  }
  
  /**
   * Gets a process ID that is nearly guaranteed to be globally unique.
   */
  public static long getGlobalProcessID() {
    return globalProcessID;
  }
  
  public static int random(int min, int max) {
    if(max <= min) {
      return min;
    }
    return Math.abs(RANDOM1.nextInt()) % (max - min) + min;
  }
}