java Hibernate UUID代码

package mypack;

import java.io.Serializable;
import java.net.InetAddress;
/**
* 唯一主键生成办法。从Hibernate中提取出来。
*/
public class UUIDGenerator {  

private static final int IP;
public static int IptoInt( byte[] bytes ) {
 int result = 0;
 for (int i=0; i<4; i++) {
  result = ( result << 8 ) - Byte.MIN_VALUE + (int) bytes[i];
 }
 return result;
}
static {
 int ipadd;
 try {
  ipadd = IptoInt( 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 UUIDGenerator() {
}  

/**
 * 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(UUIDGenerator.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();
}  

private final static String sep = "";  

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();
}  

public Serializable 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 args[]) throws Exception {
UUIDGenerator t=new UUIDGenerator();
System.out.println(t.generate().toString()); //4028be81421ea40a01421ea40aea0000
}