1/* 2 * Copyright (c) 2003, 2014, 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 26package java.util; 27 28import java.security.*; 29 30import jdk.internal.misc.JavaLangAccess; 31import jdk.internal.misc.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 */ 73public 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 len = name.length(); 198 if (len > 36) { 199 throw new IllegalArgumentException("UUID string too large"); 200 } 201 202 int dash1 = name.indexOf('-', 0); 203 int dash2 = name.indexOf('-', dash1 + 1); 204 int dash3 = name.indexOf('-', dash2 + 1); 205 int dash4 = name.indexOf('-', dash3 + 1); 206 int dash5 = name.indexOf('-', dash4 + 1); 207 208 // For any valid input, dash1 through dash4 will be positive and dash5 209 // negative, but it's enough to check dash4 and dash5: 210 // - if dash1 is -1, dash4 will be -1 211 // - if dash1 is positive but dash2 is -1, dash4 will be -1 212 // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be 213 // positive, but so will dash5 214 if (dash4 < 0 || dash5 >= 0) { 215 throw new IllegalArgumentException("Invalid UUID string: " + name); 216 } 217 218 long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL; 219 mostSigBits <<= 16; 220 mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL; 221 mostSigBits <<= 16; 222 mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL; 223 long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL; 224 leastSigBits <<= 48; 225 leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL; 226 227 return new UUID(mostSigBits, leastSigBits); 228 } 229 230 // Field Accessor Methods 231 232 /** 233 * Returns the least significant 64 bits of this UUID's 128 bit value. 234 * 235 * @return The least significant 64 bits of this UUID's 128 bit value 236 */ 237 public long getLeastSignificantBits() { 238 return leastSigBits; 239 } 240 241 /** 242 * Returns the most significant 64 bits of this UUID's 128 bit value. 243 * 244 * @return The most significant 64 bits of this UUID's 128 bit value 245 */ 246 public long getMostSignificantBits() { 247 return mostSigBits; 248 } 249 250 /** 251 * The version number associated with this {@code UUID}. The version 252 * number describes how this {@code UUID} was generated. 253 * 254 * The version number has the following meaning: 255 * <ul> 256 * <li>1 Time-based UUID 257 * <li>2 DCE security UUID 258 * <li>3 Name-based UUID 259 * <li>4 Randomly generated UUID 260 * </ul> 261 * 262 * @return The version number of this {@code UUID} 263 */ 264 public int version() { 265 // Version is bits masked by 0x000000000000F000 in MS long 266 return (int)((mostSigBits >> 12) & 0x0f); 267 } 268 269 /** 270 * The variant number associated with this {@code UUID}. The variant 271 * number describes the layout of the {@code UUID}. 272 * 273 * The variant number has the following meaning: 274 * <ul> 275 * <li>0 Reserved for NCS backward compatibility 276 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a> 277 * (Leach-Salz), used by this class 278 * <li>6 Reserved, Microsoft Corporation backward compatibility 279 * <li>7 Reserved for future definition 280 * </ul> 281 * 282 * @return The variant number of this {@code UUID} 283 */ 284 public int variant() { 285 // This field is composed of a varying number of bits. 286 // 0 - - Reserved for NCS backward compatibility 287 // 1 0 - The IETF aka Leach-Salz variant (used by this class) 288 // 1 1 0 Reserved, Microsoft backward compatibility 289 // 1 1 1 Reserved for future definition. 290 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62))) 291 & (leastSigBits >> 63)); 292 } 293 294 /** 295 * The timestamp value associated with this UUID. 296 * 297 * <p> The 60 bit timestamp value is constructed from the time_low, 298 * time_mid, and time_hi fields of this {@code UUID}. The resulting 299 * timestamp is measured in 100-nanosecond units since midnight, 300 * October 15, 1582 UTC. 301 * 302 * <p> The timestamp value is only meaningful in a time-based UUID, which 303 * has version type 1. If this {@code UUID} is not a time-based UUID then 304 * this method throws UnsupportedOperationException. 305 * 306 * @throws UnsupportedOperationException 307 * If this UUID is not a version 1 UUID 308 * @return The timestamp of this {@code UUID}. 309 */ 310 public long timestamp() { 311 if (version() != 1) { 312 throw new UnsupportedOperationException("Not a time-based UUID"); 313 } 314 315 return (mostSigBits & 0x0FFFL) << 48 316 | ((mostSigBits >> 16) & 0x0FFFFL) << 32 317 | mostSigBits >>> 32; 318 } 319 320 /** 321 * The clock sequence value associated with this UUID. 322 * 323 * <p> The 14 bit clock sequence value is constructed from the clock 324 * sequence field of this UUID. The clock sequence field is used to 325 * guarantee temporal uniqueness in a time-based UUID. 326 * 327 * <p> The {@code clockSequence} value is only meaningful in a time-based 328 * UUID, which has version type 1. If this UUID is not a time-based UUID 329 * then this method throws UnsupportedOperationException. 330 * 331 * @return The clock sequence of this {@code UUID} 332 * 333 * @throws UnsupportedOperationException 334 * If this UUID is not a version 1 UUID 335 */ 336 public int clockSequence() { 337 if (version() != 1) { 338 throw new UnsupportedOperationException("Not a time-based UUID"); 339 } 340 341 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48); 342 } 343 344 /** 345 * The node value associated with this UUID. 346 * 347 * <p> The 48 bit node value is constructed from the node field of this 348 * UUID. This field is intended to hold the IEEE 802 address of the machine 349 * that generated this UUID to guarantee spatial uniqueness. 350 * 351 * <p> The node value is only meaningful in a time-based UUID, which has 352 * version type 1. If this UUID is not a time-based UUID then this method 353 * throws UnsupportedOperationException. 354 * 355 * @return The node value of this {@code UUID} 356 * 357 * @throws UnsupportedOperationException 358 * If this UUID is not a version 1 UUID 359 */ 360 public long node() { 361 if (version() != 1) { 362 throw new UnsupportedOperationException("Not a time-based UUID"); 363 } 364 365 return leastSigBits & 0x0000FFFFFFFFFFFFL; 366 } 367 368 // Object Inherited Methods 369 370 /** 371 * Returns a {@code String} object representing this {@code UUID}. 372 * 373 * <p> The UUID string representation is as described by this BNF: 374 * <blockquote><pre> 375 * {@code 376 * UUID = <time_low> "-" <time_mid> "-" 377 * <time_high_and_version> "-" 378 * <variant_and_sequence> "-" 379 * <node> 380 * time_low = 4*<hexOctet> 381 * time_mid = 2*<hexOctet> 382 * time_high_and_version = 2*<hexOctet> 383 * variant_and_sequence = 2*<hexOctet> 384 * node = 6*<hexOctet> 385 * hexOctet = <hexDigit><hexDigit> 386 * hexDigit = 387 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" 388 * | "a" | "b" | "c" | "d" | "e" | "f" 389 * | "A" | "B" | "C" | "D" | "E" | "F" 390 * }</pre></blockquote> 391 * 392 * @return A string representation of this {@code UUID} 393 */ 394 public String toString() { 395 return jla.fastUUID(leastSigBits, mostSigBits); 396 } 397 398 /** 399 * Returns a hash code for this {@code UUID}. 400 * 401 * @return A hash code value for this {@code UUID} 402 */ 403 public int hashCode() { 404 long hilo = mostSigBits ^ leastSigBits; 405 return ((int)(hilo >> 32)) ^ (int) hilo; 406 } 407 408 /** 409 * Compares this object to the specified object. The result is {@code 410 * true} if and only if the argument is not {@code null}, is a {@code UUID} 411 * object, has the same variant, and contains the same value, bit for bit, 412 * as this {@code UUID}. 413 * 414 * @param obj 415 * The object to be compared 416 * 417 * @return {@code true} if the objects are the same; {@code false} 418 * otherwise 419 */ 420 public boolean equals(Object obj) { 421 if ((null == obj) || (obj.getClass() != UUID.class)) 422 return false; 423 UUID id = (UUID)obj; 424 return (mostSigBits == id.mostSigBits && 425 leastSigBits == id.leastSigBits); 426 } 427 428 // Comparison Operations 429 430 /** 431 * Compares this UUID with the specified UUID. 432 * 433 * <p> The first of two UUIDs is greater than the second if the most 434 * significant field in which the UUIDs differ is greater for the first 435 * UUID. 436 * 437 * @param val 438 * {@code UUID} to which this {@code UUID} is to be compared 439 * 440 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or 441 * greater than {@code val} 442 * 443 */ 444 public int compareTo(UUID val) { 445 // The ordering is intentionally set up so that the UUIDs 446 // can simply be numerically compared as two numbers 447 return (this.mostSigBits < val.mostSigBits ? -1 : 448 (this.mostSigBits > val.mostSigBits ? 1 : 449 (this.leastSigBits < val.leastSigBits ? -1 : 450 (this.leastSigBits > val.leastSigBits ? 1 : 451 0)))); 452 } 453} 454