不知大家在写数据库程序的时候使用什么做主键，使用无意义的东东做主键是个很好的做法，很多人用SEQUENCE，可我觉得Hibernate中的UUID是个不错的选择，我把他剥出来，喜欢的人可以拿去用。
算法如下：
package com.xxh.hz.util;
import java.io.Serializable;
import java.net.InetAddress;
/**
* 唯一主键生成办法。从Hibernate中提取出来。我一直觉得这不错，不用建什么Sequence * @version : V1.0 * @author : 王力猛(Email: wallimn@sohu.com QQ: 54871876) * @date : 2006-12-8 下午11:51:43
*/
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(); }}
