1 /* 2 * Copyright (c) 2003, 2019, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 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. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 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). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 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 import jdk.internal.access.JavaLangAccess; 31 import jdk.internal.access.SharedSecrets; 32 33 /** 34 * A class that represents an immutable universally unique identifier (UUID). 35 * A UUID represents a 128-bit value. 36 * 37 * <p> There exist different variants of these global identifiers. The methods 38 * of this class are for manipulating the Leach-Salz variant, although the 39 * constructors allow the creation of any variant of UUID (described below). 40 * 41 * <p> The layout of a variant 2 (Leach-Salz) UUID is as follows: 42 * 43 * The most significant long consists of the following unsigned fields: 44 * <pre> 45 * 0xFFFFFFFF00000000 time_low 46 * 0x00000000FFFF0000 time_mid 47 * 0x000000000000F000 version 48 * 0x0000000000000FFF time_hi 49 * </pre> 50 * The least significant long consists of the following unsigned fields: 51 * <pre> 52 * 0xC000000000000000 variant 53 * 0x3FFF000000000000 clock_seq 54 * 0x0000FFFFFFFFFFFF node 55 * </pre> 56 * 57 * <p> The variant field contains a value which identifies the layout of the 58 * {@code UUID}. The bit layout described above is valid only for a {@code 59 * UUID} with a variant value of 2, which indicates the Leach-Salz variant. 60 * 61 * <p> The version field holds a value that describes the type of this {@code 62 * UUID}. There are four different basic types of UUIDs: time-based, DCE 63 * security, name-based, and randomly generated UUIDs. These types have a 64 * version value of 1, 2, 3 and 4, respectively. 65 * 66 * <p> For more information including algorithms used to create {@code UUID}s, 67 * see <a href="http://www.ietf.org/rfc/rfc4122.txt"> <i>RFC 4122: A 68 * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2 69 * "Algorithms for Creating a Time-Based UUID". 70 * 71 * @since 1.5 72 */ 73 public final class UUID implements java.io.Serializable, Comparable<UUID> { 74 75 /** 76 * Explicit serialVersionUID for interoperability. 77 */ 78 @java.io.Serial 79 private static final long serialVersionUID = -4856846361193249489L; 80 81 /* 82 * The most significant 64 bits of this UUID. 83 * 84 * @serial 85 */ 86 private final long mostSigBits; 87 88 /* 89 * The least significant 64 bits of this UUID. 90 * 91 * @serial 92 */ 93 private final long leastSigBits; 94 95 private static final JavaLangAccess jla = SharedSecrets.getJavaLangAccess(); 96 97 /* 98 * The random number generator used by this class to create random 99 * based UUIDs. In a holder class to defer initialization until needed. 100 */ 101 private static class Holder { 102 static final SecureRandom numberGenerator = new SecureRandom(); 103 } 104 105 // Constructors and Factories 106 107 /* 108 * Private constructor which uses a byte array to construct the new UUID. 109 */ 110 private UUID(byte[] data) { 111 long msb = 0; 112 long lsb = 0; 113 assert data.length == 16 : "data must be 16 bytes in length"; 114 for (int i=0; i<8; i++) 115 msb = (msb << 8) | (data[i] & 0xff); 116 for (int i=8; i<16; i++) 117 lsb = (lsb << 8) | (data[i] & 0xff); 118 this.mostSigBits = msb; 119 this.leastSigBits = lsb; 120 } 121 122 /** 123 * Constructs a new {@code UUID} using the specified data. {@code 124 * mostSigBits} is used for the most significant 64 bits of the {@code 125 * UUID} and {@code leastSigBits} becomes the least significant 64 bits of 126 * the {@code UUID}. 127 * 128 * @param mostSigBits 129 * The most significant bits of the {@code UUID} 130 * 131 * @param leastSigBits 132 * The least significant bits of the {@code UUID} 133 */ 134 public UUID(long mostSigBits, long leastSigBits) { 135 this.mostSigBits = mostSigBits; 136 this.leastSigBits = leastSigBits; 137 } 138 139 /** 140 * Static factory to retrieve a type 4 (pseudo randomly generated) UUID. 141 * 142 * The {@code UUID} is generated using a cryptographically strong pseudo 143 * random number generator. 144 * 145 * @return A randomly generated {@code UUID} 146 */ 147 public static UUID randomUUID() { 148 SecureRandom ng = Holder.numberGenerator; 149 150 byte[] randomBytes = new byte[16]; 151 ng.nextBytes(randomBytes); 152 randomBytes[6] &= 0x0f; /* clear version */ 153 randomBytes[6] |= 0x40; /* set to version 4 */ 154 randomBytes[8] &= 0x3f; /* clear variant */ 155 randomBytes[8] |= 0x80; /* set to IETF variant */ 156 return new UUID(randomBytes); 157 } 158 159 /** 160 * Static factory to retrieve a type 3 (name based) {@code UUID} based on 161 * the specified byte array. 162 * 163 * @param name 164 * A byte array to be used to construct a {@code UUID} 165 * 166 * @return A {@code UUID} generated from the specified array 167 */ 168 public static UUID nameUUIDFromBytes(byte[] name) { 169 MessageDigest md; 170 try { 171 md = MessageDigest.getInstance("MD5"); 172 } catch (NoSuchAlgorithmException nsae) { 173 throw new InternalError("MD5 not supported", nsae); 174 } 175 byte[] md5Bytes = md.digest(name); 176 md5Bytes[6] &= 0x0f; /* clear version */ 177 md5Bytes[6] |= 0x30; /* set to version 3 */ 178 md5Bytes[8] &= 0x3f; /* clear variant */ 179 md5Bytes[8] |= 0x80; /* set to IETF variant */ 180 return new UUID(md5Bytes); 181 } 182 183 private static final byte[] NIBBLES; 184 static { 185 byte[] ns = new byte[256]; 186 Arrays.fill(ns, (byte) -1); 187 ns['0'] = 0; 188 ns['1'] = 1; 189 ns['2'] = 2; 190 ns['3'] = 3; 191 ns['4'] = 4; 192 ns['5'] = 5; 193 ns['6'] = 6; 194 ns['7'] = 7; 195 ns['8'] = 8; 196 ns['9'] = 9; 197 ns['A'] = 10; 198 ns['B'] = 11; 199 ns['C'] = 12; 200 ns['D'] = 13; 201 ns['E'] = 14; 202 ns['F'] = 15; 203 ns['a'] = 10; 204 ns['b'] = 11; 205 ns['c'] = 12; 206 ns['d'] = 13; 207 ns['e'] = 14; 208 ns['f'] = 15; 209 NIBBLES = ns; 210 } 211 212 private static long parse4Nibbles(String name, int pos) { 213 byte[] ns = NIBBLES; 214 char ch1 = name.charAt(pos); 215 char ch2 = name.charAt(pos + 1); 216 char ch3 = name.charAt(pos + 2); 217 char ch4 = name.charAt(pos + 3); 218 return (ch1 | ch2 | ch3 | ch4) > 0xff ? 219 -1 : ns[ch1] << 12 | ns[ch2] << 8 | ns[ch3] << 4 | ns[ch4]; 220 } 221 222 /** 223 * Creates a {@code UUID} from the string standard representation as 224 * described in the {@link #toString} method. 225 * 226 * @param name 227 * A string that specifies a {@code UUID} 228 * 229 * @return A {@code UUID} with the specified value 230 * 231 * @throws IllegalArgumentException 232 * If name does not conform to the string representation as 233 * described in {@link #toString} 234 * 235 */ 236 public static UUID fromString(String name) { 237 if (name.length() == 36) { 238 char ch1 = name.charAt(8); 239 char ch2 = name.charAt(13); 240 char ch3 = name.charAt(18); 241 char ch4 = name.charAt(23); 242 if (ch1 == '-' && ch2 == '-' && ch3 == '-' && ch4 == '-') { 243 long msb1 = parse4Nibbles(name, 0); 244 long msb2 = parse4Nibbles(name, 4); 245 long msb3 = parse4Nibbles(name, 9); 246 long msb4 = parse4Nibbles(name, 14); 247 long lsb1 = parse4Nibbles(name, 19); 248 long lsb2 = parse4Nibbles(name, 24); 249 long lsb3 = parse4Nibbles(name, 28); 250 long lsb4 = parse4Nibbles(name, 32); 251 if ((msb1 | msb2 | msb3 | msb4 | lsb1 | lsb2 | lsb3 | lsb4) >= 0) { 252 return new UUID( 253 msb1 << 48 | msb2 << 32 | msb3 << 16 | msb4, 254 lsb1 << 48 | lsb2 << 32 | lsb3 << 16 | lsb4); 255 } 256 } 257 } 258 return fromString1(name); 259 } 260 261 private static UUID fromString1(String name) { 262 int len = name.length(); 263 if (len > 36) { 264 throw new IllegalArgumentException("UUID string too large"); 265 } 266 267 int dash1 = name.indexOf('-', 0); 268 int dash2 = name.indexOf('-', dash1 + 1); 269 int dash3 = name.indexOf('-', dash2 + 1); 270 int dash4 = name.indexOf('-', dash3 + 1); 271 int dash5 = name.indexOf('-', dash4 + 1); 272 273 // For any valid input, dash1 through dash4 will be positive and dash5 274 // negative, but it's enough to check dash4 and dash5: 275 // - if dash1 is -1, dash4 will be -1 276 // - if dash1 is positive but dash2 is -1, dash4 will be -1 277 // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be 278 // positive, but so will dash5 279 if (dash4 < 0 || dash5 >= 0) { 280 throw new IllegalArgumentException("Invalid UUID string: " + name); 281 } 282 283 long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL; 284 mostSigBits <<= 16; 285 mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL; 286 mostSigBits <<= 16; 287 mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL; 288 long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL; 289 leastSigBits <<= 48; 290 leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL; 291 292 return new UUID(mostSigBits, leastSigBits); 293 } 294 295 // Field Accessor Methods 296 297 /** 298 * Returns the least significant 64 bits of this UUID's 128 bit value. 299 * 300 * @return The least significant 64 bits of this UUID's 128 bit value 301 */ 302 public long getLeastSignificantBits() { 303 return leastSigBits; 304 } 305 306 /** 307 * Returns the most significant 64 bits of this UUID's 128 bit value. 308 * 309 * @return The most significant 64 bits of this UUID's 128 bit value 310 */ 311 public long getMostSignificantBits() { 312 return mostSigBits; 313 } 314 315 /** 316 * The version number associated with this {@code UUID}. The version 317 * number describes how this {@code UUID} was generated. 318 * 319 * The version number has the following meaning: 320 * <ul> 321 * <li>1 Time-based UUID 322 * <li>2 DCE security UUID 323 * <li>3 Name-based UUID 324 * <li>4 Randomly generated UUID 325 * </ul> 326 * 327 * @return The version number of this {@code UUID} 328 */ 329 public int version() { 330 // Version is bits masked by 0x000000000000F000 in MS long 331 return (int)((mostSigBits >> 12) & 0x0f); 332 } 333 334 /** 335 * The variant number associated with this {@code UUID}. The variant 336 * number describes the layout of the {@code UUID}. 337 * 338 * The variant number has the following meaning: 339 * <ul> 340 * <li>0 Reserved for NCS backward compatibility 341 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a> 342 * (Leach-Salz), used by this class 343 * <li>6 Reserved, Microsoft Corporation backward compatibility 344 * <li>7 Reserved for future definition 345 * </ul> 346 * 347 * @return The variant number of this {@code UUID} 348 */ 349 public int variant() { 350 // This field is composed of a varying number of bits. 351 // 0 - - Reserved for NCS backward compatibility 352 // 1 0 - The IETF aka Leach-Salz variant (used by this class) 353 // 1 1 0 Reserved, Microsoft backward compatibility 354 // 1 1 1 Reserved for future definition. 355 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62))) 356 & (leastSigBits >> 63)); 357 } 358 359 /** 360 * The timestamp value associated with this UUID. 361 * 362 * <p> The 60 bit timestamp value is constructed from the time_low, 363 * time_mid, and time_hi fields of this {@code UUID}. The resulting 364 * timestamp is measured in 100-nanosecond units since midnight, 365 * October 15, 1582 UTC. 366 * 367 * <p> The timestamp value is only meaningful in a time-based UUID, which 368 * has version type 1. If this {@code UUID} is not a time-based UUID then 369 * this method throws UnsupportedOperationException. 370 * 371 * @throws UnsupportedOperationException 372 * If this UUID is not a version 1 UUID 373 * @return The timestamp of this {@code UUID}. 374 */ 375 public long timestamp() { 376 if (version() != 1) { 377 throw new UnsupportedOperationException("Not a time-based UUID"); 378 } 379 380 return (mostSigBits & 0x0FFFL) << 48 381 | ((mostSigBits >> 16) & 0x0FFFFL) << 32 382 | mostSigBits >>> 32; 383 } 384 385 /** 386 * The clock sequence value associated with this UUID. 387 * 388 * <p> The 14 bit clock sequence value is constructed from the clock 389 * sequence field of this UUID. The clock sequence field is used to 390 * guarantee temporal uniqueness in a time-based UUID. 391 * 392 * <p> The {@code clockSequence} value is only meaningful in a time-based 393 * UUID, which has version type 1. If this UUID is not a time-based UUID 394 * then this method throws UnsupportedOperationException. 395 * 396 * @return The clock sequence of this {@code UUID} 397 * 398 * @throws UnsupportedOperationException 399 * If this UUID is not a version 1 UUID 400 */ 401 public int clockSequence() { 402 if (version() != 1) { 403 throw new UnsupportedOperationException("Not a time-based UUID"); 404 } 405 406 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48); 407 } 408 409 /** 410 * The node value associated with this UUID. 411 * 412 * <p> The 48 bit node value is constructed from the node field of this 413 * UUID. This field is intended to hold the IEEE 802 address of the machine 414 * that generated this UUID to guarantee spatial uniqueness. 415 * 416 * <p> The node value is only meaningful in a time-based UUID, which has 417 * version type 1. If this UUID is not a time-based UUID then this method 418 * throws UnsupportedOperationException. 419 * 420 * @return The node value of this {@code UUID} 421 * 422 * @throws UnsupportedOperationException 423 * If this UUID is not a version 1 UUID 424 */ 425 public long node() { 426 if (version() != 1) { 427 throw new UnsupportedOperationException("Not a time-based UUID"); 428 } 429 430 return leastSigBits & 0x0000FFFFFFFFFFFFL; 431 } 432 433 // Object Inherited Methods 434 435 /** 436 * Returns a {@code String} object representing this {@code UUID}. 437 * 438 * <p> The UUID string representation is as described by this BNF: 439 * <blockquote><pre> 440 * {@code 441 * UUID = <time_low> "-" <time_mid> "-" 442 * <time_high_and_version> "-" 443 * <variant_and_sequence> "-" 444 * <node> 445 * time_low = 4*<hexOctet> 446 * time_mid = 2*<hexOctet> 447 * time_high_and_version = 2*<hexOctet> 448 * variant_and_sequence = 2*<hexOctet> 449 * node = 6*<hexOctet> 450 * hexOctet = <hexDigit><hexDigit> 451 * hexDigit = 452 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" 453 * | "a" | "b" | "c" | "d" | "e" | "f" 454 * | "A" | "B" | "C" | "D" | "E" | "F" 455 * }</pre></blockquote> 456 * 457 * @return A string representation of this {@code UUID} 458 */ 459 public String toString() { 460 return jla.fastUUID(leastSigBits, mostSigBits); 461 } 462 463 /** 464 * Returns a hash code for this {@code UUID}. 465 * 466 * @return A hash code value for this {@code UUID} 467 */ 468 public int hashCode() { 469 long hilo = mostSigBits ^ leastSigBits; 470 return ((int)(hilo >> 32)) ^ (int) hilo; 471 } 472 473 /** 474 * Compares this object to the specified object. The result is {@code 475 * true} if and only if the argument is not {@code null}, is a {@code UUID} 476 * object, has the same variant, and contains the same value, bit for bit, 477 * as this {@code UUID}. 478 * 479 * @param obj 480 * The object to be compared 481 * 482 * @return {@code true} if the objects are the same; {@code false} 483 * otherwise 484 */ 485 public boolean equals(Object obj) { 486 if ((null == obj) || (obj.getClass() != UUID.class)) 487 return false; 488 UUID id = (UUID)obj; 489 return (mostSigBits == id.mostSigBits && 490 leastSigBits == id.leastSigBits); 491 } 492 493 // Comparison Operations 494 495 /** 496 * Compares this UUID with the specified UUID. 497 * 498 * <p> The first of two UUIDs is greater than the second if the most 499 * significant field in which the UUIDs differ is greater for the first 500 * UUID. 501 * 502 * @param val 503 * {@code UUID} to which this {@code UUID} is to be compared 504 * 505 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or 506 * greater than {@code val} 507 * 508 */ 509 public int compareTo(UUID val) { 510 // The ordering is intentionally set up so that the UUIDs 511 // can simply be numerically compared as two numbers 512 return (this.mostSigBits < val.mostSigBits ? -1 : 513 (this.mostSigBits > val.mostSigBits ? 1 : 514 (this.leastSigBits < val.leastSigBits ? -1 : 515 (this.leastSigBits > val.leastSigBits ? 1 : 516 0)))); 517 } 518 }