/* * Copyright (c) 2003, 2011, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util; import java.security.*; /** * A class that represents an immutable universally unique identifier (UUID). * A UUID represents a 128-bit value. * * <p> There exist different variants of these global identifiers.  The methods * of this class are for manipulating the Leach-Salz variant, although the * constructors allow the creation of any variant of UUID (described below). * * <p> The layout of a variant 2 (Leach-Salz) UUID is as follows: * * The most significant long consists of the following unsigned fields: * <pre> * 0xFFFFFFFF00000000 time_low * 0x00000000FFFF0000 time_mid * 0x000000000000F000 version * 0x0000000000000FFF time_hi * </pre> * The least significant long consists of the following unsigned fields: * <pre> * 0xC000000000000000 variant * 0x3FFF000000000000 clock_seq * 0x0000FFFFFFFFFFFF node * </pre> * * <p> The variant field contains a value which identifies the layout of the * {@code UUID}.  The bit layout described above is valid only for a {@code * UUID} with a variant value of 2, which indicates the Leach-Salz variant. * * <p> The version field holds a value that describes the type of this {@code * UUID}.  There are four different basic types of UUIDs: time-based, DCE * security, name-based, and randomly generated UUIDs.  These types have a * version value of 1, 2, 3 and 4, respectively. * * <p> For more information including algorithms used to create {@code UUID}s, * see <a href="http://www.ietf.org/rfc/rfc4122.txt"> <i>RFC&nbsp;4122: A * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2 * &quot;Algorithms for Creating a Time-Based UUID&quot;. * * @since   1.5 */public final class UUID implements java.io.Serializable, Comparable<UUID> {     /**     * Explicit serialVersionUID for interoperability.     */    private static final long serialVersionUID = -4856846361193249489L;     /*     * The most significant 64 bits of this UUID.     *     * @serial     */    private final long mostSigBits;     /*     * The least significant 64 bits of this UUID.     *     * @serial     */    private final long leastSigBits;     /*     * The random number generator used by this class to create random     * based UUIDs.     */    private static volatile SecureRandom numberGenerator = null;     // Constructors and Factories     /*     * Private constructor which uses a byte array to construct the new UUID.     */    private UUID(byte[] data) {        long msb = 0;        long lsb = 0;        assert data.length == 16 : "data must be 16 bytes in length";        for (int i=0; i<8; i++)            msb = (msb << 8) | (data[i] & 0xff);        for (int i=8; i<16; i++)            lsb = (lsb << 8) | (data[i] & 0xff);        this.mostSigBits = msb;        this.leastSigBits = lsb;    }     /**     * Constructs a new {@code UUID} using the specified data.  {@code     * mostSigBits} is used for the most significant 64 bits of the {@code     * UUID} and {@code leastSigBits} becomes the least significant 64 bits of     * the {@code UUID}.     *     * @param  mostSigBits     *         The most significant bits of the {@code UUID}     *     * @param  leastSigBits     *         The least significant bits of the {@code UUID}     */    public UUID(long mostSigBits, long leastSigBits) {        this.mostSigBits = mostSigBits;        this.leastSigBits = leastSigBits;    }     /**     * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.     *     * The {@code UUID} is generated using a cryptographically strong pseudo     * random number generator.     *     * @return  A randomly generated {@code UUID}     */    public static UUID randomUUID() {        SecureRandom ng = numberGenerator;        if (ng == null) {            numberGenerator = ng = new SecureRandom();        }         byte[] randomBytes = new byte[16];        ng.nextBytes(randomBytes);        randomBytes[6]  &= 0x0f;  /* clear version        */        randomBytes[6]  |= 0x40;  /* set to version 4     */        randomBytes[8]  &= 0x3f;  /* clear variant        */        randomBytes[8]  |= 0x80;  /* set to IETF variant  */        return new UUID(randomBytes);    }     /**     * Static factory to retrieve a type 3 (name based) {@code UUID} based on     * the specified byte array.     *     * @param  name     *         A byte array to be used to construct a {@code UUID}     *     * @return  A {@code UUID} generated from the specified array     */    public static UUID nameUUIDFromBytes(byte[] name) {        MessageDigest md;        try {            md = MessageDigest.getInstance("MD5");        } catch (NoSuchAlgorithmException nsae) {            throw new InternalError("MD5 not supported");        }        byte[] md5Bytes = md.digest(name);        md5Bytes[6]  &= 0x0f;  /* clear version        */        md5Bytes[6]  |= 0x30;  /* set to version 3     */        md5Bytes[8]  &= 0x3f;  /* clear variant        */        md5Bytes[8]  |= 0x80;  /* set to IETF variant  */        return new UUID(md5Bytes);    }     /**     * Creates a {@code UUID} from the string standard representation as     * described in the {@link #toString} method.     *     * @param  name     *         A string that specifies a {@code UUID}     *     * @return  A {@code UUID} with the specified value     *     * @throws  IllegalArgumentException     *          If name does not conform to the string representation as     *          described in {@link #toString}     *     */    public static UUID fromString(String name) {        String[] components = name.split("-");        if (components.length != 5)            throw new IllegalArgumentException("Invalid UUID string: "+name);        for (int i=0; i<5; i++)            components[i] = "0x"+components[i];         long mostSigBits = Long.decode(components[0]).longValue();        mostSigBits <<= 16;        mostSigBits |= Long.decode(components[1]).longValue();        mostSigBits <<= 16;        mostSigBits |= Long.decode(components[2]).longValue();         long leastSigBits = Long.decode(components[3]).longValue();        leastSigBits <<= 48;        leastSigBits |= Long.decode(components[4]).longValue();         return new UUID(mostSigBits, leastSigBits);    }     // Field Accessor Methods     /**     * Returns the least significant 64 bits of this UUID's 128 bit value.     *     * @return  The least significant 64 bits of this UUID's 128 bit value     */    public long getLeastSignificantBits() {        return leastSigBits;    }     /**     * Returns the most significant 64 bits of this UUID's 128 bit value.     *     * @return  The most significant 64 bits of this UUID's 128 bit value     */    public long getMostSignificantBits() {        return mostSigBits;    }     /**     * The version number associated with this {@code UUID}.  The version     * number describes how this {@code UUID} was generated.     *     * The version number has the following meaning:     * <p><ul>     * <li>1    Time-based UUID     * <li>2    DCE security UUID     * <li>3    Name-based UUID     * <li>4    Randomly generated UUID     * </ul>     *     * @return  The version number of this {@code UUID}     */    public int version() {        // Version is bits masked by 0x000000000000F000 in MS long        return (int)((mostSigBits >> 12) & 0x0f);    }     /**     * The variant number associated with this {@code UUID}.  The variant     * number describes the layout of the {@code UUID}.     *     * The variant number has the following meaning:     * <p><ul>     * <li>0    Reserved for NCS backward compatibility     * <li>2    The Leach-Salz variant (used by this class)     * <li>6    Reserved, Microsoft Corporation backward compatibility     * <li>7    Reserved for future definition     * </ul>     *     * @return  The variant number of this {@code UUID}     */    public int variant() {        // This field is composed of a varying number of bits.        // 0    -    -    Reserved for NCS backward compatibility        // 1    0    -    The Leach-Salz variant (used by this class)        // 1    1    0    Reserved, Microsoft backward compatibility        // 1    1    1    Reserved for future definition.        return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))                      & (leastSigBits >> 63));    }     /**     * The timestamp value associated with this UUID.     *     * <p> The 60 bit timestamp value is constructed from the time_low,     * time_mid, and time_hi fields of this {@code UUID}.  The resulting     * timestamp is measured in 100-nanosecond units since midnight,     * October 15, 1582 UTC.     *     * <p> The timestamp value is only meaningful in a time-based UUID, which     * has version type 1.  If this {@code UUID} is not a time-based UUID then     * this method throws UnsupportedOperationException.     *     * @throws UnsupportedOperationException     *         If this UUID is not a version 1 UUID     */    public long timestamp() {        if (version() != 1) {            throw new UnsupportedOperationException("Not a time-based UUID");        }         return (mostSigBits & 0x0FFFL) << 48             | ((mostSigBits >> 16) & 0x0FFFFL) << 32             | mostSigBits >>> 32;    }     /**     * The clock sequence value associated with this UUID.     *     * <p> The 14 bit clock sequence value is constructed from the clock     * sequence field of this UUID.  The clock sequence field is used to     * guarantee temporal uniqueness in a time-based UUID.     *     * <p> The {@code clockSequence} value is only meaningful in a time-based     * UUID, which has version type 1.  If this UUID is not a time-based UUID     * then this method throws UnsupportedOperationException.     *     * @return  The clock sequence of this {@code UUID}     *     * @throws  UnsupportedOperationException     *          If this UUID is not a version 1 UUID     */    public int clockSequence() {        if (version() != 1) {            throw new UnsupportedOperationException("Not a time-based UUID");        }         return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);    }     /**     * The node value associated with this UUID.     *     * <p> The 48 bit node value is constructed from the node field of this     * UUID.  This field is intended to hold the IEEE 802 address of the machine     * that generated this UUID to guarantee spatial uniqueness.     *     * <p> The node value is only meaningful in a time-based UUID, which has     * version type 1.  If this UUID is not a time-based UUID then this method     * throws UnsupportedOperationException.     *     * @return  The node value of this {@code UUID}     *     * @throws  UnsupportedOperationException     *          If this UUID is not a version 1 UUID     */    public long node() {        if (version() != 1) {            throw new UnsupportedOperationException("Not a time-based UUID");        }         return leastSigBits & 0x0000FFFFFFFFFFFFL;    }     // Object Inherited Methods     /**     * Returns a {@code String} object representing this {@code UUID}.     *     * <p> The UUID string representation is as described by this BNF:     * <blockquote><pre>     * {@code     * UUID                   = <time_low> "-" <time_mid> "-"     *                          <time_high_and_version> "-"     *                          <variant_and_sequence> "-"     *                          <node>     * time_low               = 4*<hexOctet>     * time_mid               = 2*<hexOctet>     * time_high_and_version  = 2*<hexOctet>     * variant_and_sequence   = 2*<hexOctet>     * node                   = 6*<hexOctet>     * hexOctet               = <hexDigit><hexDigit>     * hexDigit               =     *       "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"     *       | "a" | "b" | "c" | "d" | "e" | "f"     *       | "A" | "B" | "C" | "D" | "E" | "F"     * }</pre></blockquote>     *     * @return  A string representation of this {@code UUID}     */    public String toString() {        return (digits(mostSigBits >> 32, 8) + "-" +                digits(mostSigBits >> 16, 4) + "-" +                digits(mostSigBits, 4) + "-" +                digits(leastSigBits >> 48, 4) + "-" +                digits(leastSigBits, 12));    }     /** Returns val represented by the specified number of hex digits. */    private static String digits(long val, int digits) {        long hi = 1L << (digits * 4);        return Long.toHexString(hi | (val & (hi - 1))).substring(1);    }     /**     * Returns a hash code for this {@code UUID}.     *     * @return  A hash code value for this {@code UUID}     */    public int hashCode() {        long hilo = mostSigBits ^ leastSigBits;        return ((int)(hilo >> 32)) ^ (int) hilo;    }     /**     * Compares this object to the specified object.  The result is {@code     * true} if and only if the argument is not {@code null}, is a {@code UUID}     * object, has the same variant, and contains the same value, bit for bit,     * as this {@code UUID}.     *     * @param  obj     *         The object to be compared     *     * @return  {@code true} if the objects are the same; {@code false}     *          otherwise     */    public boolean equals(Object obj) {        if ((null == obj) || (obj.getClass() != UUID.class))            return false;        UUID id = (UUID)obj;        return (mostSigBits == id.mostSigBits &&                leastSigBits == id.leastSigBits);    }     // Comparison Operations     /**     * Compares this UUID with the specified UUID.     *     * <p> The first of two UUIDs is greater than the second if the most     * significant field in which the UUIDs differ is greater for the first     * UUID.     *     * @param  val     *         {@code UUID} to which this {@code UUID} is to be compared     *     * @return  -1, 0 or 1 as this {@code UUID} is less than, equal to, or     *          greater than {@code val}     *     */    public int compareTo(UUID val) {        // The ordering is intentionally set up so that the UUIDs        // can simply be numerically compared as two numbers        return (this.mostSigBits < val.mostSigBits ? -1 :                (this.mostSigBits > val.mostSigBits ? 1 :                 (this.leastSigBits < val.leastSigBits ? -1 :                  (this.leastSigBits > val.leastSigBits ? 1 :                   0))));    }}