UUID 의 알고리즘

import java.net.InetAddress;

public class UUIDHexGenerator {
private String sep = "";

private static final int IP;

private static short counter = (short) 0;

private static final int JVM = (int) (System.currentTimeMillis() >>> 8);

private static UUIDHexGenerator uuidgen = new UUIDHexGenerator();

static {

   int ipadd;
   try {
    ipadd = toInt(InetAddress.getLocalHost().getAddress());
   } catch (Exception e) {
    ipadd = 0;
   }
   IP = ipadd;
}

public static UUIDHexGenerator getInstance() {
   return uuidgen;
}

public static int toInt(byte[] bytes) {
   int result = 0;
   for (int i = 0; i < 4; i++) {
    result = (result << 8) - Byte.MIN_VALUE + (int) bytes[i];
   }
   return result;
}

protected String format(int intval) {
   String formatted = Integer.toHexString(intval);
   StringBuffer buf = new StringBuffer("00000000");
   buf.replace(8 - formatted.length(), 8, formatted);
   return buf.toString();
}

protected String format(short shortval) {
   String formatted = Integer.toHexString(shortval);
   StringBuffer buf = new StringBuffer("0000");
   buf.replace(4 - formatted.length(), 4, formatted);
   return buf.toString();
}

protected int getJVM() {
   return JVM;
}

protected synchronized short getCount() {
   if (counter < 0) {
    counter = 0;
   }
   return counter++;
}

protected int getIP() {
   return IP;
}

protected short getHiTime() {
   return (short) (System.currentTimeMillis() >>> 32);
}

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

public String generate() {
   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();
}

// public static void main(String[] str) {
//   UUIDHexGenerator id = new UUIDHexGenerator();
//   for (int i = 0; i <= 100; i++) {
//    System.out.println(id.generate());
//   }
// }

}