java中生成UUID

GUID号称可以做到一台机器每秒产生10000000个GUID，则可以保证3240年不重复（不过只是概率意义上），不知哪位大侠有能力验证，或者将证明方法告知，感激不尽！至于UUID是什么自已问搜索引擎吧


１．在Java1.5中，已经包含了一个UUID的实现java.util.UUID。要随机生成一个UUID，只要用两行代码就可以了：String uuid = UUID.randonUUID().toString();
２．如果是jdk1.5以下版本，可以采用一个开源实现：http://jug.safehaus.org/ 或者用jakarta commons下的http://jakarta.apache.org/commons/sandbox/id/
３．如果系统中采用了Hibernate框架，也可以用Hibernate的UUIDHexGenerator。如：String uuid = (String) new UUIDHexGenerator().generate(null, null);
附带UUID的生成算法：
import java.io.Serializable;
import java.net.InetAddress;
import org.hibernate.id.UUIDHexGenerator;
/**
* 唯一主键生成办法。从Hibernate中提取出来。
* @version : V1.0
* @author : 王力猛
*/
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;
}
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();
}
//测试
// public static void main(String[] str) {
// UUIDHexGenerator id = new UUIDHexGenerator();
// for (int i = 0; i <= 100; i++) {
// System.out.println(id.generate());
// }
// }
}