java中的uuid ，guid算法

java中的uuid ，guid算法

import java.io.*;

import java.security.*;

public final class UUID

    implements Serializable, Comparable

{

    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");

        }

       //juapk.com

        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 StringBuilder())

.append("Invalid UUID string: ").append(s).toString());

        for(int i = 0; i < 5; i++)

            as[i] = (new StringBuilder()).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 StringBuilder()).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);

    }

    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();

}

直接调用里边方法就得到唯一的串了