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

}