JAVA UUID [转]
UUID(Universally Unique Identifier)全局唯一标识符,是指在一台机器上生成的数字，它保证对在同一时空中的所有机器都是唯一的。按照开放软件基金会(OSF)制定的标准计算，用到了以太网卡地址、纳秒级时间、芯片ID码和许多可能的数字。由以下几部分的组合：当前日期和时间(UUID的第一个部分与时间有关，如果你在生成一个UUID之后，过几秒又生成一个UUID，则第一个部分不同，其余相同)，时钟序列，全局唯一的IEEE机器识别号（如果有网卡，从网卡获得，没有网卡以其他方式获得），UUID的唯一缺陷在于生成的结果串会比较长。
在Java中生成UUID主要有以下几种方式:
1. JDK1.5
如果使用的JDK1.5的话,那么生成UUID变成了一件简单的事,以为JDK实现了UUID: java.util.UUID,直接调用即可.
2. 第三方开源类库(推荐使用):
最著名的是 JUG .特点上是: 纯Java实现，开源，LGPL协议。采用了Native的方式产生真正的Uuid.而且提供了不同平台的实现,包括:
- Linux / x86
- Windows (98, ME, NT, 2K, XP?) / x86
- Solaris / Sparc
- Mac OS X
- FreeBSD / x86
import org.doomdark.uuid.UUIDGenerator;
UUIDGenerator generator = UUIDGenerator.getInstance();
UUID uuid = generator.generateRandomBasedUUID();
3. Java代码实现（jdk1.4可运行）:
import java.io.IOException; import java.io.ObjectInputStream; import java.io.Serializable; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.util.ArrayList; import java.util.HashSet; import java.util.Iterator; import java.util.List; import java.util.Set; public final class UUID implements Serializable, Comparable { private static final long serialVersionUID = 0xbc9903f7986d852fL; private final long mostSigBits; private final long leastSigBits; private transient int version; private transient int variant; private volatile transient long timestamp; private transient int sequence; private transient long node; private transient int hashCode; private static volatile SecureRandom numberGenerator = null; // static final boolean $assertionsDisabled = !UUID.desiredAssertionStatus(); public static void main(String[] args) { System.out.println(UUID.randomUUID()); List list = new ArrayList(); String uid = ""; for (int i = 0; i < 100000; i++) { uid = UUID.randomUUID().toString(); list.add(uid); } System.out.println(list.size()); removeDuplicateObj(list); } private static void removeDuplicateObj(List list) { Set someSet = new HashSet(list); Iterator iterator = someSet.iterator(); List tempList = new ArrayList(); int i = 0; while (iterator.hasNext()) { tempList.add(iterator.next().toString()); i++; } System.out.println(tempList.size()); } private UUID(byte abyte0[]) { version = -1; variant = -1; timestamp = -1L; sequence = -1; node = -1L; hashCode = -1; long l = 0L; long l1 = 0L; // if(!$assertionsDisabled && abyte0.length != 16) // throw new AssertionError(); for(int i = 0; i < 8; i++) l = l << 8 | (long)(abyte0[i] & 0xff); for(int j = 8; j < 16; j++) l1 = l1 << 8 | (long)(abyte0[j] & 0xff); mostSigBits = l; leastSigBits = l1; } public UUID(long l, long l1) { version = -1; variant = -1; timestamp = -1L; sequence = -1; node = -1L; hashCode = -1; mostSigBits = l; leastSigBits = l1; } public static UUID randomUUID() { SecureRandom securerandom = numberGenerator; if(securerandom == null) numberGenerator = securerandom = new SecureRandom(); byte abyte0[] = new byte[16]; securerandom.nextBytes(abyte0); abyte0[6] &= 0xf; abyte0[6] |= 0x40; abyte0[8] &= 0x3f; abyte0[8] |= 0x80; UUID uuid = new UUID(abyte0); return new UUID(abyte0); } public static UUID nameUUIDFromBytes(byte abyte0[]) { MessageDigest messagedigest; try { messagedigest = MessageDigest.getInstance("MD5"); } catch(NoSuchAlgorithmException nosuchalgorithmexception) { throw new InternalError("MD5 not supported"); } byte abyte1[] = messagedigest.digest(abyte0); abyte1[6] &= 0xf; abyte1[6] |= 0x30; abyte1[8] &= 0x3f; abyte1[8] |= 0x80; return new UUID(abyte1); } public static UUID fromString(String s) { String as[] = s.split("-"); if(as.length != 5) throw new IllegalArgumentException((new StringBuffer()) .append("Invalid UUID string: ").append(s).toString()); for(int i = 0; i < 5; i++) as[i] = (new StringBuffer()).append("0x").append(as[i]).toString(); long l = Long.decode(as[0]).longValue(); l <<= 16; l |= Long.decode(as[1]).longValue(); l <<= 16; l |= Long.decode(as[2]).longValue(); long l1 = Long.decode(as[3]).longValue(); l1 <<= 48; l1 |= Long.decode(as[4]).longValue(); return new UUID(l, l1); } public long getLeastSignificantBits() { return leastSigBits; } public long getMostSignificantBits() { return mostSigBits; } public int version() { if(version < 0) version = (int)(mostSigBits >> 12 & 15L); return version; } public int variant() { if(variant < 0) if(leastSigBits >>> 63 == 0L) variant = 0; else if(leastSigBits >>> 62 == 2L) variant = 2; else variant = (int)(leastSigBits >>> 61); return variant; } public long timestamp() { if(version() != 1) throw new UnsupportedOperationException("Not a time-based UUID"); long l = timestamp; if(l < 0L) { l = (mostSigBits & 4095L) << 48; l |= (mostSigBits >> 16 & 65535L) << 32; l |= mostSigBits >>> 32; timestamp = l; } return l; } public int clockSequence() { if(version() != 1) throw new UnsupportedOperationException("Not a time-based UUID"); if(sequence < 0) sequence = (int)((leastSigBits & 0x3fff000000000000L) >>> 48); return sequence; } public long node() { if(version() != 1) throw new UnsupportedOperationException("Not a time-based UUID"); if(node < 0L) node = leastSigBits & 0xffffffffffffL; return node; } public String toString() { return (new StringBuffer()).append(digits(mostSigBits >> 32, 8)).append("-").append(digits(mostSigBits >> 16, 4)) .append("-").append(digits(mostSigBits, 4)).append("-") .append(digits(leastSigBits >> 48, 4)).append("-").append(digits(leastSigBits, 12)).toString(); } private static String digits(long l, int i) { long l1 = 1L << i * 4; return Long.toHexString(l1 | l & l1 - 1L).substring(1); } public int hashCode() { if(hashCode == -1) hashCode = (int)(mostSigBits >> 32 ^ mostSigBits ^ leastSigBits >> 32 ^ leastSigBits); return hashCode; } public boolean equals(Object obj) { if(!(obj instanceof UUID)) return false; if(((UUID)obj).variant() != variant()) { return false; } else { UUID uuid = (UUID)obj; return mostSigBits == uuid.mostSigBits && leastSigBits == uuid.leastSigBits; } } public int compareTo(UUID uuid) { return mostSigBits >= uuid.mostSigBits ? mostSigBits <= uuid.mostSigBits ? leastSigBits >= uuid.leastSigBits ? ((byte) (((byte)(leastSigBits <= uuid.leastSigBits ? 0 : 1)))) : -1 : 1 : -1; } private void readObject(ObjectInputStream objectinputstream) throws IOException, ClassNotFoundException { objectinputstream.defaultReadObject(); version = -1; variant = -1; timestamp = -1L; sequence = -1; node = -1L; hashCode = -1; } public int compareTo(Object obj) { return compareTo((UUID)obj); } }
转自：http://spiritfrog.iteye.com/blog/604048
uuid的代码还没来得及看。。。