1 /* 2 * Copyright (c) 2003, 2013, 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 /** 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 4122: A 65 * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2 66 * "Algorithms for Creating a Time-Based UUID". 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. In a holder class to defer initialization until needed. 94 */ 95 private static class Holder { 96 static final SecureRandom numberGenerator = new SecureRandom(); 97 } 98 99 // Constructors and Factories 100 101 /* 102 * Private constructor which uses a byte array to construct the new UUID. 103 */ UUID(byte[] data)104 private UUID(byte[] data) { 105 long msb = 0; 106 long lsb = 0; 107 assert data.length == 16 : "data must be 16 bytes in length"; 108 for (int i=0; i<8; i++) 109 msb = (msb << 8) | (data[i] & 0xff); 110 for (int i=8; i<16; i++) 111 lsb = (lsb << 8) | (data[i] & 0xff); 112 this.mostSigBits = msb; 113 this.leastSigBits = lsb; 114 } 115 116 /** 117 * Constructs a new {@code UUID} using the specified data. {@code 118 * mostSigBits} is used for the most significant 64 bits of the {@code 119 * UUID} and {@code leastSigBits} becomes the least significant 64 bits of 120 * the {@code UUID}. 121 * 122 * @param mostSigBits 123 * The most significant bits of the {@code UUID} 124 * 125 * @param leastSigBits 126 * The least significant bits of the {@code UUID} 127 */ UUID(long mostSigBits, long leastSigBits)128 public UUID(long mostSigBits, long leastSigBits) { 129 this.mostSigBits = mostSigBits; 130 this.leastSigBits = leastSigBits; 131 } 132 133 /** 134 * Static factory to retrieve a type 4 (pseudo randomly generated) UUID. 135 * 136 * The {@code UUID} is generated using a cryptographically strong pseudo 137 * random number generator. 138 * 139 * @return A randomly generated {@code UUID} 140 */ randomUUID()141 public static UUID randomUUID() { 142 SecureRandom ng = Holder.numberGenerator; 143 144 byte[] randomBytes = new byte[16]; 145 ng.nextBytes(randomBytes); 146 randomBytes[6] &= 0x0f; /* clear version */ 147 randomBytes[6] |= 0x40; /* set to version 4 */ 148 randomBytes[8] &= 0x3f; /* clear variant */ 149 randomBytes[8] |= 0x80; /* set to IETF variant */ 150 return new UUID(randomBytes); 151 } 152 153 /** 154 * Static factory to retrieve a type 3 (name based) {@code UUID} based on 155 * the specified byte array. 156 * 157 * @param name 158 * A byte array to be used to construct a {@code UUID} 159 * 160 * @return A {@code UUID} generated from the specified array 161 */ nameUUIDFromBytes(byte[] name)162 public static UUID nameUUIDFromBytes(byte[] name) { 163 MessageDigest md; 164 try { 165 md = MessageDigest.getInstance("MD5"); 166 } catch (NoSuchAlgorithmException nsae) { 167 throw new InternalError("MD5 not supported", nsae); 168 } 169 byte[] md5Bytes = md.digest(name); 170 md5Bytes[6] &= 0x0f; /* clear version */ 171 md5Bytes[6] |= 0x30; /* set to version 3 */ 172 md5Bytes[8] &= 0x3f; /* clear variant */ 173 md5Bytes[8] |= 0x80; /* set to IETF variant */ 174 return new UUID(md5Bytes); 175 } 176 177 /** 178 * Creates a {@code UUID} from the string standard representation as 179 * described in the {@link #toString} method. 180 * 181 * @param name 182 * A string that specifies a {@code UUID} 183 * 184 * @return A {@code UUID} with the specified value 185 * 186 * @throws IllegalArgumentException 187 * If name does not conform to the string representation as 188 * described in {@link #toString} 189 * 190 */ fromString(String name)191 public static UUID fromString(String name) { 192 String[] components = name.split("-"); 193 if (components.length != 5) 194 throw new IllegalArgumentException("Invalid UUID string: "+name); 195 for (int i=0; i<5; i++) 196 components[i] = "0x"+components[i]; 197 198 long mostSigBits = Long.decode(components[0]).longValue(); 199 mostSigBits <<= 16; 200 mostSigBits |= Long.decode(components[1]).longValue(); 201 mostSigBits <<= 16; 202 mostSigBits |= Long.decode(components[2]).longValue(); 203 204 long leastSigBits = Long.decode(components[3]).longValue(); 205 leastSigBits <<= 48; 206 leastSigBits |= Long.decode(components[4]).longValue(); 207 208 return new UUID(mostSigBits, leastSigBits); 209 } 210 211 // Field Accessor Methods 212 213 /** 214 * Returns the least significant 64 bits of this UUID's 128 bit value. 215 * 216 * @return The least significant 64 bits of this UUID's 128 bit value 217 */ getLeastSignificantBits()218 public long getLeastSignificantBits() { 219 return leastSigBits; 220 } 221 222 /** 223 * Returns the most significant 64 bits of this UUID's 128 bit value. 224 * 225 * @return The most significant 64 bits of this UUID's 128 bit value 226 */ getMostSignificantBits()227 public long getMostSignificantBits() { 228 return mostSigBits; 229 } 230 231 /** 232 * The version number associated with this {@code UUID}. The version 233 * number describes how this {@code UUID} was generated. 234 * 235 * The version number has the following meaning: 236 * <ul> 237 * <li>1 Time-based UUID 238 * <li>2 DCE security UUID 239 * <li>3 Name-based UUID 240 * <li>4 Randomly generated UUID 241 * </ul> 242 * 243 * @return The version number of this {@code UUID} 244 */ version()245 public int version() { 246 // Version is bits masked by 0x000000000000F000 in MS long 247 return (int)((mostSigBits >> 12) & 0x0f); 248 } 249 250 /** 251 * The variant number associated with this {@code UUID}. The variant 252 * number describes the layout of the {@code UUID}. 253 * 254 * The variant number has the following meaning: 255 * <ul> 256 * <li>0 Reserved for NCS backward compatibility 257 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a> 258 * (Leach-Salz), 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 */ variant()265 public int variant() { 266 // This field is composed of a varying number of bits. 267 // 0 - - Reserved for NCS backward compatibility 268 // 1 0 - The IETF aka Leach-Salz variant (used by this class) 269 // 1 1 0 Reserved, Microsoft backward compatibility 270 // 1 1 1 Reserved for future definition. 271 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62))) 272 & (leastSigBits >> 63)); 273 } 274 275 /** 276 * The timestamp value associated with this UUID. 277 * 278 * <p> The 60 bit timestamp value is constructed from the time_low, 279 * time_mid, and time_hi fields of this {@code UUID}. The resulting 280 * timestamp is measured in 100-nanosecond units since midnight, 281 * October 15, 1582 UTC. 282 * 283 * <p> The timestamp value is only meaningful in a time-based UUID, which 284 * has version type 1. If this {@code UUID} is not a time-based UUID then 285 * this method throws UnsupportedOperationException. 286 * 287 * @throws UnsupportedOperationException 288 * If this UUID is not a version 1 UUID 289 * @return The timestamp of this {@code UUID}. 290 */ timestamp()291 public long timestamp() { 292 if (version() != 1) { 293 throw new UnsupportedOperationException("Not a time-based UUID"); 294 } 295 296 return (mostSigBits & 0x0FFFL) << 48 297 | ((mostSigBits >> 16) & 0x0FFFFL) << 32 298 | mostSigBits >>> 32; 299 } 300 301 /** 302 * The clock sequence value associated with this UUID. 303 * 304 * <p> The 14 bit clock sequence value is constructed from the clock 305 * sequence field of this UUID. The clock sequence field is used to 306 * guarantee temporal uniqueness in a time-based UUID. 307 * 308 * <p> The {@code clockSequence} value is only meaningful in a time-based 309 * UUID, which has version type 1. If this UUID is not a time-based UUID 310 * then this method throws UnsupportedOperationException. 311 * 312 * @return The clock sequence of this {@code UUID} 313 * 314 * @throws UnsupportedOperationException 315 * If this UUID is not a version 1 UUID 316 */ clockSequence()317 public int clockSequence() { 318 if (version() != 1) { 319 throw new UnsupportedOperationException("Not a time-based UUID"); 320 } 321 322 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48); 323 } 324 325 /** 326 * The node value associated with this UUID. 327 * 328 * <p> The 48 bit node value is constructed from the node field of this 329 * UUID. This field is intended to hold the IEEE 802 address of the machine 330 * that generated this UUID to guarantee spatial uniqueness. 331 * 332 * <p> The node value is only meaningful in a time-based UUID, which has 333 * version type 1. If this UUID is not a time-based UUID then this method 334 * throws UnsupportedOperationException. 335 * 336 * @return The node value of this {@code UUID} 337 * 338 * @throws UnsupportedOperationException 339 * If this UUID is not a version 1 UUID 340 */ node()341 public long node() { 342 if (version() != 1) { 343 throw new UnsupportedOperationException("Not a time-based UUID"); 344 } 345 346 return leastSigBits & 0x0000FFFFFFFFFFFFL; 347 } 348 349 // Object Inherited Methods 350 351 /** 352 * Returns a {@code String} object representing this {@code UUID}. 353 * 354 * <p> The UUID string representation is as described by this BNF: 355 * <blockquote><pre> 356 * {@code 357 * UUID = <time_low> "-" <time_mid> "-" 358 * <time_high_and_version> "-" 359 * <variant_and_sequence> "-" 360 * <node> 361 * time_low = 4*<hexOctet> 362 * time_mid = 2*<hexOctet> 363 * time_high_and_version = 2*<hexOctet> 364 * variant_and_sequence = 2*<hexOctet> 365 * node = 6*<hexOctet> 366 * hexOctet = <hexDigit><hexDigit> 367 * hexDigit = 368 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" 369 * | "a" | "b" | "c" | "d" | "e" | "f" 370 * | "A" | "B" | "C" | "D" | "E" | "F" 371 * }</pre></blockquote> 372 * 373 * @return A string representation of this {@code UUID} 374 */ toString()375 public String toString() { 376 return (digits(mostSigBits >> 32, 8) + "-" + 377 digits(mostSigBits >> 16, 4) + "-" + 378 digits(mostSigBits, 4) + "-" + 379 digits(leastSigBits >> 48, 4) + "-" + 380 digits(leastSigBits, 12)); 381 } 382 383 /** Returns val represented by the specified number of hex digits. */ digits(long val, int digits)384 private static String digits(long val, int digits) { 385 long hi = 1L << (digits * 4); 386 return Long.toHexString(hi | (val & (hi - 1))).substring(1); 387 } 388 389 /** 390 * Returns a hash code for this {@code UUID}. 391 * 392 * @return A hash code value for this {@code UUID} 393 */ hashCode()394 public int hashCode() { 395 long hilo = mostSigBits ^ leastSigBits; 396 return ((int)(hilo >> 32)) ^ (int) hilo; 397 } 398 399 /** 400 * Compares this object to the specified object. The result is {@code 401 * true} if and only if the argument is not {@code null}, is a {@code UUID} 402 * object, has the same variant, and contains the same value, bit for bit, 403 * as this {@code UUID}. 404 * 405 * @param obj 406 * The object to be compared 407 * 408 * @return {@code true} if the objects are the same; {@code false} 409 * otherwise 410 */ equals(Object obj)411 public boolean equals(Object obj) { 412 if ((null == obj) || (obj.getClass() != UUID.class)) 413 return false; 414 UUID id = (UUID)obj; 415 return (mostSigBits == id.mostSigBits && 416 leastSigBits == id.leastSigBits); 417 } 418 419 // Comparison Operations 420 421 /** 422 * Compares this UUID with the specified UUID. 423 * 424 * <p> The first of two UUIDs is greater than the second if the most 425 * significant field in which the UUIDs differ is greater for the first 426 * UUID. 427 * 428 * @param val 429 * {@code UUID} to which this {@code UUID} is to be compared 430 * 431 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or 432 * greater than {@code val} 433 * 434 */ compareTo(UUID val)435 public int compareTo(UUID val) { 436 // The ordering is intentionally set up so that the UUIDs 437 // can simply be numerically compared as two numbers 438 return (this.mostSigBits < val.mostSigBits ? -1 : 439 (this.mostSigBits > val.mostSigBits ? 1 : 440 (this.leastSigBits < val.leastSigBits ? -1 : 441 (this.leastSigBits > val.leastSigBits ? 1 : 442 0)))); 443 } 444 } 445