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 private static final long serialVersionUID = -4856846361193249489L; 79 80 /* 81 * The most significant 64 bits of this UUID. 82 * 83 * @serial 84 */ 85 private final long mostSigBits; 86 87 /* 88 * The least significant 64 bits of this UUID. 89 * 90 * @serial 91 */ 92 private final long leastSigBits; 93 94 private static final JavaLangAccess jla = SharedSecrets.getJavaLangAccess(); 95 96 /* 97 * The random number generator used by this class to create random 98 * based UUIDs. In a holder class to defer initialization until needed. 99 */ 100 private static class Holder { 101 static final SecureRandom numberGenerator = new SecureRandom(); 102 } 103 104 // Constructors and Factories 105 106 /* 107 * Private constructor which uses a byte array to construct the new UUID. 108 */ 109 private UUID(byte[] data) { 110 long msb = 0; 111 long lsb = 0; 112 assert data.length == 16 : "data must be 16 bytes in length"; 113 for (int i=0; i<8; i++) 114 msb = (msb << 8) | (data[i] & 0xff); 115 for (int i=8; i<16; i++) 116 lsb = (lsb << 8) | (data[i] & 0xff); 117 this.mostSigBits = msb; 118 this.leastSigBits = lsb; 119 } 120 121 /** 122 * Constructs a new {@code UUID} using the specified data. {@code 123 * mostSigBits} is used for the most significant 64 bits of the {@code 124 * UUID} and {@code leastSigBits} becomes the least significant 64 bits of 125 * the {@code UUID}. 126 * 127 * @param mostSigBits 128 * The most significant bits of the {@code UUID} 129 * 130 * @param leastSigBits 131 * The least significant bits of the {@code UUID} 132 */ 133 public UUID(long mostSigBits, long leastSigBits) { 134 this.mostSigBits = mostSigBits; 135 this.leastSigBits = leastSigBits; 136 } 137 138 /** 139 * Static factory to retrieve a type 4 (pseudo randomly generated) UUID. 140 * 141 * The {@code UUID} is generated using a cryptographically strong pseudo 142 * random number generator. 143 * 144 * @return A randomly generated {@code UUID} 145 */ 146 public static UUID randomUUID() { 147 SecureRandom ng = Holder.numberGenerator; 148 149 byte[] randomBytes = new byte[16]; 150 ng.nextBytes(randomBytes); 151 randomBytes[6] &= 0x0f; /* clear version */ 152 randomBytes[6] |= 0x40; /* set to version 4 */ 153 randomBytes[8] &= 0x3f; /* clear variant */ 154 randomBytes[8] |= 0x80; /* set to IETF variant */ 155 return new UUID(randomBytes); 156 } 157 158 /** 159 * Static factory to retrieve a type 3 (name based) {@code UUID} based on 160 * the specified byte array. 161 * 162 * @param name 163 * A byte array to be used to construct a {@code UUID} 164 * 165 * @return A {@code UUID} generated from the specified array 166 */ 167 public static UUID nameUUIDFromBytes(byte[] name) { 168 MessageDigest md; 169 try { 170 md = MessageDigest.getInstance("MD5"); 171 } catch (NoSuchAlgorithmException nsae) { 172 throw new InternalError("MD5 not supported", nsae); 173 } 174 byte[] md5Bytes = md.digest(name); 175 md5Bytes[6] &= 0x0f; /* clear version */ 176 md5Bytes[6] |= 0x30; /* set to version 3 */ 177 md5Bytes[8] &= 0x3f; /* clear variant */ 178 md5Bytes[8] |= 0x80; /* set to IETF variant */ 179 return new UUID(md5Bytes); 180 } 181 182 /** 183 * Creates a {@code UUID} from the string standard representation as 184 * described in the {@link #toString} method. 185 * 186 * @param name 187 * A string that specifies a {@code UUID} 188 * 189 * @return A {@code UUID} with the specified value 190 * 191 * @throws IllegalArgumentException 192 * If name does not conform to the string representation as 193 * described in {@link #toString} 194 * 195 */ 196 public static UUID fromString(String name) { 197 int dash1 = name.indexOf('-', 0); 198 int dash2 = name.indexOf('-', dash1 + 1); 199 int dash3 = name.indexOf('-', dash2 + 1); 200 int dash4 = name.indexOf('-', dash3 + 1); 201 int dash5 = name.indexOf('-', dash4 + 1); 202 203 // For any valid input, dash1 through dash4 will be positive and dash5 204 // negative, but it's enough to check dash4 and dash5: 205 // - if dash1 is -1, dash4 will be -1 206 // - if dash1 is positive but dash2 is -1, dash4 will be -1 207 // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be 208 // positive, but so will dash5 209 210 if (dash4 > 0 && dash5 < 0) { 211 long x1 = Long.parseLong(name, 0, dash1, 16); 212 long x2 = Long.parseLong(name, dash1 + 1, dash2, 16); 213 long x3 = Long.parseLong(name, dash2 + 1, dash3, 16); 214 long x4 = Long.parseLong(name, dash3 + 1, dash4, 16); 215 long x5 = Long.parseLong(name, dash4 + 1, name.length(), 16); 216 217 if (((x1 >> 32) | ((x2 | x3 | x4) >> 16) | (x5 >> 48)) == 0L) { 218 return new UUID((x1 << 32) | (x2 << 16) | x3, (x4 << 48) | x5); 219 } 220 } 221 throw new IllegalArgumentException("Invalid UUID string: " + name); 222 } 223 224 // Field Accessor Methods 225 226 /** 227 * Returns the least significant 64 bits of this UUID's 128 bit value. 228 * 229 * @return The least significant 64 bits of this UUID's 128 bit value 230 */ 231 public long getLeastSignificantBits() { 232 return leastSigBits; 233 } 234 235 /** 236 * Returns the most significant 64 bits of this UUID's 128 bit value. 237 * 238 * @return The most significant 64 bits of this UUID's 128 bit value 239 */ 240 public long getMostSignificantBits() { 241 return mostSigBits; 242 } 243 244 /** 245 * The version number associated with this {@code UUID}. The version 246 * number describes how this {@code UUID} was generated. 247 * 248 * The version number has the following meaning: 249 * <ul> 250 * <li>1 Time-based UUID 251 * <li>2 DCE security UUID 252 * <li>3 Name-based UUID 253 * <li>4 Randomly generated UUID 254 * </ul> 255 * 256 * @return The version number of this {@code UUID} 257 */ 258 public int version() { 259 // Version is bits masked by 0x000000000000F000 in MS long 260 return (int)((mostSigBits >> 12) & 0x0f); 261 } 262 263 /** 264 * The variant number associated with this {@code UUID}. The variant 265 * number describes the layout of the {@code UUID}. 266 * 267 * The variant number has the following meaning: 268 * <ul> 269 * <li>0 Reserved for NCS backward compatibility 270 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a> 271 * (Leach-Salz), used by this class 272 * <li>6 Reserved, Microsoft Corporation backward compatibility 273 * <li>7 Reserved for future definition 274 * </ul> 275 * 276 * @return The variant number of this {@code UUID} 277 */ 278 public int variant() { 279 // This field is composed of a varying number of bits. 280 // 0 - - Reserved for NCS backward compatibility 281 // 1 0 - The IETF aka Leach-Salz variant (used by this class) 282 // 1 1 0 Reserved, Microsoft backward compatibility 283 // 1 1 1 Reserved for future definition. 284 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62))) 285 & (leastSigBits >> 63)); 286 } 287 288 /** 289 * The timestamp value associated with this UUID. 290 * 291 * <p> The 60 bit timestamp value is constructed from the time_low, 292 * time_mid, and time_hi fields of this {@code UUID}. The resulting 293 * timestamp is measured in 100-nanosecond units since midnight, 294 * October 15, 1582 UTC. 295 * 296 * <p> The timestamp value is only meaningful in a time-based UUID, which 297 * has version type 1. If this {@code UUID} is not a time-based UUID then 298 * this method throws UnsupportedOperationException. 299 * 300 * @throws UnsupportedOperationException 301 * If this UUID is not a version 1 UUID 302 * @return The timestamp of this {@code UUID}. 303 */ 304 public long timestamp() { 305 if (version() != 1) { 306 throw new UnsupportedOperationException("Not a time-based UUID"); 307 } 308 309 return (mostSigBits & 0x0FFFL) << 48 310 | ((mostSigBits >> 16) & 0x0FFFFL) << 32 311 | mostSigBits >>> 32; 312 } 313 314 /** 315 * The clock sequence value associated with this UUID. 316 * 317 * <p> The 14 bit clock sequence value is constructed from the clock 318 * sequence field of this UUID. The clock sequence field is used to 319 * guarantee temporal uniqueness in a time-based UUID. 320 * 321 * <p> The {@code clockSequence} value is only meaningful in a time-based 322 * UUID, which has version type 1. If this UUID is not a time-based UUID 323 * then this method throws UnsupportedOperationException. 324 * 325 * @return The clock sequence of this {@code UUID} 326 * 327 * @throws UnsupportedOperationException 328 * If this UUID is not a version 1 UUID 329 */ 330 public int clockSequence() { 331 if (version() != 1) { 332 throw new UnsupportedOperationException("Not a time-based UUID"); 333 } 334 335 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48); 336 } 337 338 /** 339 * The node value associated with this UUID. 340 * 341 * <p> The 48 bit node value is constructed from the node field of this 342 * UUID. This field is intended to hold the IEEE 802 address of the machine 343 * that generated this UUID to guarantee spatial uniqueness. 344 * 345 * <p> The node value is only meaningful in a time-based UUID, which has 346 * version type 1. If this UUID is not a time-based UUID then this method 347 * throws UnsupportedOperationException. 348 * 349 * @return The node value of this {@code UUID} 350 * 351 * @throws UnsupportedOperationException 352 * If this UUID is not a version 1 UUID 353 */ 354 public long node() { 355 if (version() != 1) { 356 throw new UnsupportedOperationException("Not a time-based UUID"); 357 } 358 359 return leastSigBits & 0x0000FFFFFFFFFFFFL; 360 } 361 362 // Object Inherited Methods 363 364 /** 365 * Returns a {@code String} object representing this {@code UUID}. 366 * 367 * <p> The UUID string representation is as described by this BNF: 368 * <blockquote><pre> 369 * {@code 370 * UUID = <time_low> "-" <time_mid> "-" 371 * <time_high_and_version> "-" 372 * <variant_and_sequence> "-" 373 * <node> 374 * time_low = 4*<hexOctet> 375 * time_mid = 2*<hexOctet> 376 * time_high_and_version = 2*<hexOctet> 377 * variant_and_sequence = 2*<hexOctet> 378 * node = 6*<hexOctet> 379 * hexOctet = <hexDigit><hexDigit> 380 * hexDigit = 381 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" 382 * | "a" | "b" | "c" | "d" | "e" | "f" 383 * | "A" | "B" | "C" | "D" | "E" | "F" 384 * }</pre></blockquote> 385 * 386 * @return A string representation of this {@code UUID} 387 */ 388 public String toString() { 389 return jla.fastUUID(leastSigBits, mostSigBits); 390 } 391 392 /** 393 * Returns a hash code for this {@code UUID}. 394 * 395 * @return A hash code value for this {@code UUID} 396 */ 397 public int hashCode() { 398 long hilo = mostSigBits ^ leastSigBits; 399 return ((int)(hilo >> 32)) ^ (int) hilo; 400 } 401 402 /** 403 * Compares this object to the specified object. The result is {@code 404 * true} if and only if the argument is not {@code null}, is a {@code UUID} 405 * object, has the same variant, and contains the same value, bit for bit, 406 * as this {@code UUID}. 407 * 408 * @param obj 409 * The object to be compared 410 * 411 * @return {@code true} if the objects are the same; {@code false} 412 * otherwise 413 */ 414 public boolean equals(Object obj) { 415 if ((null == obj) || (obj.getClass() != UUID.class)) 416 return false; 417 UUID id = (UUID)obj; 418 return (mostSigBits == id.mostSigBits && 419 leastSigBits == id.leastSigBits); 420 } 421 422 // Comparison Operations 423 424 /** 425 * Compares this UUID with the specified UUID. 426 * 427 * <p> The first of two UUIDs is greater than the second if the most 428 * significant field in which the UUIDs differ is greater for the first 429 * UUID. 430 * 431 * @param val 432 * {@code UUID} to which this {@code UUID} is to be compared 433 * 434 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or 435 * greater than {@code val} 436 * 437 */ 438 public int compareTo(UUID val) { 439 // The ordering is intentionally set up so that the UUIDs 440 // can simply be numerically compared as two numbers 441 return (this.mostSigBits < val.mostSigBits ? -1 : 442 (this.mostSigBits > val.mostSigBits ? 1 : 443 (this.leastSigBits < val.leastSigBits ? -1 : 444 (this.leastSigBits > val.leastSigBits ? 1 : 445 0)))); 446 } 447 }