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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
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   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
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  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
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  17  * You should have received a copy of the GNU General Public License version
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  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.util;
  27 
  28 import java.security.*;
  29 
  30 /**
  31  * A class that represents an immutable universally unique identifier (UUID).
  32  * A UUID represents a 128-bit value.
  33  *
  34  * <p> There exist different variants of these global identifiers.  The methods
  35  * of this class are for manipulating the Leach-Salz variant, although the
  36  * constructors allow the creation of any variant of UUID (described below).
  37  *
  38  * <p> The layout of a variant 2 (Leach-Salz) UUID is as follows:
  39  *
  40  * The most significant long consists of the following unsigned fields:
  41  * <pre>
  42  * 0xFFFFFFFF00000000 time_low
  43  * 0x00000000FFFF0000 time_mid
  44  * 0x000000000000F000 version
  45  * 0x0000000000000FFF time_hi
  46  * </pre>
  47  * The least significant long consists of the following unsigned fields:
  48  * <pre>
  49  * 0xC000000000000000 variant
  50  * 0x3FFF000000000000 clock_seq
  51  * 0x0000FFFFFFFFFFFF node
  52  * </pre>
  53  *
  54  * <p> The variant field contains a value which identifies the layout of the
  55  * {@code UUID}.  The bit layout described above is valid only for a {@code
  56  * UUID} with a variant value of 2, which indicates the Leach-Salz variant.
  57  *
  58  * <p> The version field holds a value that describes the type of this {@code
  59  * UUID}.  There are four different basic types of UUIDs: time-based, DCE
  60  * security, name-based, and randomly generated UUIDs.  These types have a
  61  * version value of 1, 2, 3 and 4, respectively.
  62  *
  63  * <p> For more information including algorithms used to create {@code UUID}s,
  64  * see <a href="http://www.ietf.org/rfc/rfc4122.txt"> <i>RFC&nbsp;4122: A
  65  * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2
  66  * &quot;Algorithms for Creating a Time-Based UUID&quot;.
  67  *
  68  * @since   1.5
  69  */
  70 public final class UUID implements java.io.Serializable, Comparable<UUID> {
  71 
  72     /**
  73      * Explicit serialVersionUID for interoperability.
  74      */
  75     private static final long serialVersionUID = -4856846361193249489L;
  76 
  77     /*
  78      * The most significant 64 bits of this UUID.
  79      *
  80      * @serial
  81      */
  82     private final long mostSigBits;
  83 
  84     /*
  85      * The least significant 64 bits of this UUID.
  86      *
  87      * @serial
  88      */
  89     private final long leastSigBits;
  90 
  91     /*
  92      * The random number generator used by this class to create random
  93      * based UUIDs.
  94      */
  95     private static volatile SecureRandom numberGenerator = null;
  96 
  97     // Constructors and Factories
  98 
  99     /*
 100      * Private constructor which uses a byte array to construct the new UUID.
 101      */
 102     private UUID(byte[] data) {
 103         long msb = 0;
 104         long lsb = 0;
 105         assert data.length == 16 : "data must be 16 bytes in length";
 106         for (int i=0; i<8; i++)
 107             msb = (msb << 8) | (data[i] & 0xff);
 108         for (int i=8; i<16; i++)
 109             lsb = (lsb << 8) | (data[i] & 0xff);
 110         this.mostSigBits = msb;
 111         this.leastSigBits = lsb;
 112     }
 113 
 114     /**
 115      * Constructs a new {@code UUID} using the specified data.  {@code
 116      * mostSigBits} is used for the most significant 64 bits of the {@code
 117      * UUID} and {@code leastSigBits} becomes the least significant 64 bits of
 118      * the {@code UUID}.
 119      *
 120      * @param  mostSigBits
 121      *         The most significant bits of the {@code UUID}
 122      *
 123      * @param  leastSigBits
 124      *         The least significant bits of the {@code UUID}
 125      */
 126     public UUID(long mostSigBits, long leastSigBits) {
 127         this.mostSigBits = mostSigBits;
 128         this.leastSigBits = leastSigBits;
 129     }
 130 
 131     /**
 132      * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
 133      *
 134      * The {@code UUID} is generated using a cryptographically strong pseudo
 135      * random number generator.
 136      *
 137      * @return  A randomly generated {@code UUID}
 138      */
 139     public static UUID randomUUID() {
 140         SecureRandom ng = numberGenerator;
 141         if (ng == null) {
 142             numberGenerator = ng = new SecureRandom();
 143         }
 144 
 145         byte[] randomBytes = new byte[16];
 146         ng.nextBytes(randomBytes);
 147         randomBytes[6]  &= 0x0f;  /* clear version        */
 148         randomBytes[6]  |= 0x40;  /* set to version 4     */
 149         randomBytes[8]  &= 0x3f;  /* clear variant        */
 150         randomBytes[8]  |= 0x80;  /* set to IETF variant  */
 151         return new UUID(randomBytes);
 152     }
 153 
 154     /**
 155      * Static factory to retrieve a type 3 (name based) {@code UUID} based on
 156      * the specified byte array.
 157      *
 158      * @param  name
 159      *         A byte array to be used to construct a {@code UUID}
 160      *
 161      * @return  A {@code UUID} generated from the specified array
 162      */
 163     public static UUID nameUUIDFromBytes(byte[] name) {
 164         MessageDigest md;
 165         try {
 166             md = MessageDigest.getInstance("MD5");
 167         } catch (NoSuchAlgorithmException nsae) {
 168             throw new InternalError("MD5 not supported");
 169         }
 170         byte[] md5Bytes = md.digest(name);
 171         md5Bytes[6]  &= 0x0f;  /* clear version        */
 172         md5Bytes[6]  |= 0x30;  /* set to version 3     */
 173         md5Bytes[8]  &= 0x3f;  /* clear variant        */
 174         md5Bytes[8]  |= 0x80;  /* set to IETF variant  */
 175         return new UUID(md5Bytes);
 176     }
 177 
 178     /**
 179      * Creates a {@code UUID} from the string standard representation as
 180      * described in the {@link #toString} method.
 181      *
 182      * @param  name
 183      *         A string that specifies a {@code UUID}
 184      *
 185      * @return  A {@code UUID} with the specified value
 186      *
 187      * @throws  IllegalArgumentException
 188      *          If name does not conform to the string representation as
 189      *          described in {@link #toString}
 190      *
 191      */
 192     public static UUID fromString(String name) {
 193         String[] components = name.split("-");
 194         if (components.length != 5)
 195             throw new IllegalArgumentException("Invalid UUID string: "+name);
 196         for (int i=0; i<5; i++)
 197             components[i] = "0x"+components[i];
 198 
 199         long mostSigBits = Long.decode(components[0]).longValue();
 200         mostSigBits <<= 16;
 201         mostSigBits |= Long.decode(components[1]).longValue();
 202         mostSigBits <<= 16;
 203         mostSigBits |= Long.decode(components[2]).longValue();
 204 
 205         long leastSigBits = Long.decode(components[3]).longValue();
 206         leastSigBits <<= 48;
 207         leastSigBits |= Long.decode(components[4]).longValue();
 208 
 209         return new UUID(mostSigBits, leastSigBits);
 210     }
 211 
 212     // Field Accessor Methods
 213 
 214     /**
 215      * Returns the least significant 64 bits of this UUID's 128 bit value.
 216      *
 217      * @return  The least significant 64 bits of this UUID's 128 bit value
 218      */
 219     public long getLeastSignificantBits() {
 220         return leastSigBits;
 221     }
 222 
 223     /**
 224      * Returns the most significant 64 bits of this UUID's 128 bit value.
 225      *
 226      * @return  The most significant 64 bits of this UUID's 128 bit value
 227      */
 228     public long getMostSignificantBits() {
 229         return mostSigBits;
 230     }
 231 
 232     /**
 233      * The version number associated with this {@code UUID}.  The version
 234      * number describes how this {@code UUID} was generated.
 235      *
 236      * The version number has the following meaning:
 237      * <p><ul>
 238      * <li>1    Time-based UUID
 239      * <li>2    DCE security UUID
 240      * <li>3    Name-based UUID
 241      * <li>4    Randomly generated UUID
 242      * </ul>
 243      *
 244      * @return  The version number of this {@code UUID}
 245      */
 246     public int version() {
 247         // Version is bits masked by 0x000000000000F000 in MS long
 248         return (int)((mostSigBits >> 12) & 0x0f);
 249     }
 250 
 251     /**
 252      * The variant number associated with this {@code UUID}.  The variant
 253      * number describes the layout of the {@code UUID}.
 254      *
 255      * The variant number has the following meaning:
 256      * <p><ul>
 257      * <li>0    Reserved for NCS backward compatibility
 258      * <li>2    The Leach-Salz variant (used by this class)
 259      * <li>6    Reserved, Microsoft Corporation backward compatibility
 260      * <li>7    Reserved for future definition
 261      * </ul>
 262      *
 263      * @return  The variant number of this {@code UUID}
 264      */
 265     public int variant() {
 266         // This field is composed of a varying number of bits
 267         return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
 268                       & (leastSigBits >> 63));
 269     }
 270 
 271     /**
 272      * The timestamp value associated with this UUID.
 273      *
 274      * <p> The 60 bit timestamp value is constructed from the time_low,
 275      * time_mid, and time_hi fields of this {@code UUID}.  The resulting
 276      * timestamp is measured in 100-nanosecond units since midnight,
 277      * October 15, 1582 UTC.
 278      *
 279      * <p> The timestamp value is only meaningful in a time-based UUID, which
 280      * has version type 1.  If this {@code UUID} is not a time-based UUID then
 281      * this method throws UnsupportedOperationException.
 282      *
 283      * @throws UnsupportedOperationException
 284      *         If this UUID is not a version 1 UUID
 285      */
 286     public long timestamp() {
 287         if (version() != 1) {
 288             throw new UnsupportedOperationException("Not a time-based UUID");
 289         }
 290 
 291         return (mostSigBits & 0x0FFFL) << 48
 292              | ((mostSigBits >> 16) & 0x0FFFFL) << 32
 293              | mostSigBits >>> 32;
 294     }
 295 
 296     /**
 297      * The clock sequence value associated with this UUID.
 298      *
 299      * <p> The 14 bit clock sequence value is constructed from the clock
 300      * sequence field of this UUID.  The clock sequence field is used to
 301      * guarantee temporal uniqueness in a time-based UUID.
 302      *
 303      * <p> The {@code clockSequence} value is only meaningful in a time-based
 304      * UUID, which has version type 1.  If this UUID is not a time-based UUID
 305      * then this method throws UnsupportedOperationException.
 306      *
 307      * @return  The clock sequence of this {@code UUID}
 308      *
 309      * @throws  UnsupportedOperationException
 310      *          If this UUID is not a version 1 UUID
 311      */
 312     public int clockSequence() {
 313         if (version() != 1) {
 314             throw new UnsupportedOperationException("Not a time-based UUID");
 315         }
 316 
 317         return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
 318     }
 319 
 320     /**
 321      * The node value associated with this UUID.
 322      *
 323      * <p> The 48 bit node value is constructed from the node field of this
 324      * UUID.  This field is intended to hold the IEEE 802 address of the machine
 325      * that generated this UUID to guarantee spatial uniqueness.
 326      *
 327      * <p> The node value is only meaningful in a time-based UUID, which has
 328      * version type 1.  If this UUID is not a time-based UUID then this method
 329      * throws UnsupportedOperationException.
 330      *
 331      * @return  The node value of this {@code UUID}
 332      *
 333      * @throws  UnsupportedOperationException
 334      *          If this UUID is not a version 1 UUID
 335      */
 336     public long node() {
 337         if (version() != 1) {
 338             throw new UnsupportedOperationException("Not a time-based UUID");
 339         }
 340 
 341         return leastSigBits & 0x0000FFFFFFFFFFFFL;
 342     }
 343 
 344     // Object Inherited Methods
 345 
 346     /**
 347      * Returns a {@code String} object representing this {@code UUID}.
 348      *
 349      * <p> The UUID string representation is as described by this BNF:
 350      * <blockquote><pre>
 351      * {@code
 352      * UUID                   = <time_low> "-" <time_mid> "-"
 353      *                          <time_high_and_version> "-"
 354      *                          <variant_and_sequence> "-"
 355      *                          <node>
 356      * time_low               = 4*<hexOctet>
 357      * time_mid               = 2*<hexOctet>
 358      * time_high_and_version  = 2*<hexOctet>
 359      * variant_and_sequence   = 2*<hexOctet>
 360      * node                   = 6*<hexOctet>
 361      * hexOctet               = <hexDigit><hexDigit>
 362      * hexDigit               =
 363      *       "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
 364      *       | "a" | "b" | "c" | "d" | "e" | "f"
 365      *       | "A" | "B" | "C" | "D" | "E" | "F"
 366      * }</pre></blockquote>
 367      *
 368      * @return  A string representation of this {@code UUID}
 369      */
 370     public String toString() {
 371         return (digits(mostSigBits >> 32, 8) + "-" +
 372                 digits(mostSigBits >> 16, 4) + "-" +
 373                 digits(mostSigBits, 4) + "-" +
 374                 digits(leastSigBits >> 48, 4) + "-" +
 375                 digits(leastSigBits, 12));
 376     }
 377 
 378     /** Returns val represented by the specified number of hex digits. */
 379     private static String digits(long val, int digits) {
 380         long hi = 1L << (digits * 4);
 381         return Long.toHexString(hi | (val & (hi - 1))).substring(1);
 382     }
 383 
 384     /**
 385      * Returns a hash code for this {@code UUID}.
 386      *
 387      * @return  A hash code value for this {@code UUID}
 388      */
 389     public int hashCode() {
 390         long hilo = mostSigBits ^ leastSigBits;
 391         return ((int)(hilo >> 32)) ^ (int) hilo;
 392     }
 393 
 394     /**
 395      * Compares this object to the specified object.  The result is {@code
 396      * true} if and only if the argument is not {@code null}, is a {@code UUID}
 397      * object, has the same variant, and contains the same value, bit for bit,
 398      * as this {@code UUID}.
 399      *
 400      * @param  obj
 401      *         The object to be compared
 402      *
 403      * @return  {@code true} if the objects are the same; {@code false}
 404      *          otherwise
 405      */
 406     public boolean equals(Object obj) {
 407         if ((null == obj) || (obj.getClass() != UUID.class))
 408             return false;
 409         UUID id = (UUID)obj;
 410         return (mostSigBits == id.mostSigBits &&
 411                 leastSigBits == id.leastSigBits);
 412     }
 413 
 414     // Comparison Operations
 415 
 416     /**
 417      * Compares this UUID with the specified UUID.
 418      *
 419      * <p> The first of two UUIDs is greater than the second if the most
 420      * significant field in which the UUIDs differ is greater for the first
 421      * UUID.
 422      *
 423      * @param  val
 424      *         {@code UUID} to which this {@code UUID} is to be compared
 425      *
 426      * @return  -1, 0 or 1 as this {@code UUID} is less than, equal to, or
 427      *          greater than {@code val}
 428      *
 429      */
 430     public int compareTo(UUID val) {
 431         // The ordering is intentionally set up so that the UUIDs
 432         // can simply be numerically compared as two numbers
 433         return (this.mostSigBits < val.mostSigBits ? -1 :
 434                 (this.mostSigBits > val.mostSigBits ? 1 :
 435                  (this.leastSigBits < val.leastSigBits ? -1 :
 436                   (this.leastSigBits > val.leastSigBits ? 1 :
 437                    0))));
 438     }
 439 }