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 /**
184 * Used by {@code fromString}. While {@code Character.digit(ch, 16)}
185 * could be used to the same effect, benchmarks show specializing
186 * for ASCII hex is still a small but significant gain. We should
187 * examine if {@code Character.digit(ch, 16)} can be optimized and
188 * this code replaced without adding any overhead.
189 */
190 private static final byte[] NIBBLES;
191
192 static {
193 byte[] ns = new byte[256];
194 java.util.Arrays.fill(ns, (byte) -1);
195 ns['0'] = 0;
196 ns['1'] = 1;
197 ns['2'] = 2;
198 ns['3'] = 3;
199 ns['4'] = 4;
200 ns['5'] = 5;
201 ns['6'] = 6;
202 ns['7'] = 7;
203 ns['8'] = 8;
204 ns['9'] = 9;
205 ns['A'] = 10;
206 ns['B'] = 11;
207 ns['C'] = 12;
208 ns['D'] = 13;
209 ns['E'] = 14;
210 ns['F'] = 15;
211 ns['a'] = 10;
212 ns['b'] = 11;
213 ns['c'] = 12;
214 ns['d'] = 13;
215 ns['e'] = 14;
216 ns['f'] = 15;
217 NIBBLES = ns;
218 }
219
220 /**
221 * Creates a {@code UUID} from the string standard representation as
222 * described in the {@link #toString} method.
223 *
224 * @param name
225 * A string that specifies a {@code UUID}
226 *
227 * @return A {@code UUID} with the specified value
228 *
229 * @throws IllegalArgumentException
230 * If name does not conform to the string representation as
231 * described in {@link #toString}
232 *
233 */
234 public static UUID fromString(String name) {
235 if (name.length() == 36) {
236 char ch1 = name.charAt(8);
237 char ch2 = name.charAt(13);
238 char ch3 = name.charAt(18);
239 char ch4 = name.charAt(23);
240 if (ch1 == '-' && ch2 == '-' && ch3 == '-' && ch4 == '-') {
241 long msb1 = parse4Nibbles(name, 0);
242 long msb2 = parse4Nibbles(name, 4);
243 long msb3 = parse4Nibbles(name, 9);
244 long msb4 = parse4Nibbles(name, 14);
245 long lsb1 = parse4Nibbles(name, 19);
246 long lsb2 = parse4Nibbles(name, 24);
247 long lsb3 = parse4Nibbles(name, 28);
248 long lsb4 = parse4Nibbles(name, 32);
249 if ((msb1 | msb2 | msb3 | msb4 | lsb1 | lsb2 | lsb3 | lsb4) >= 0) {
250 return new UUID(
251 msb1 << 48 | msb2 << 32 | msb3 << 16 | msb4,
252 lsb1 << 48 | lsb2 << 32 | lsb3 << 16 | lsb4);
253 }
254 }
255 }
256 return fromString1(name);
257 }
258
259 private static long parse4Nibbles(String name, int pos) {
260 byte[] ns = NIBBLES;
261 char ch1 = name.charAt(pos);
262 char ch2 = name.charAt(pos + 1);
263 char ch3 = name.charAt(pos + 2);
264 char ch4 = name.charAt(pos + 3);
265 return (ch1 | ch2 | ch3 | ch4) > 0xff ?
266 -1 : ns[ch1] << 12 | ns[ch2] << 8 | ns[ch3] << 4 | ns[ch4];
267 }
268
269 private static UUID fromString1(String name) {
270 int len = name.length();
271 if (len > 36) {
272 throw new IllegalArgumentException("UUID string too large");
273 }
274
275 int dash1 = name.indexOf('-', 0);
276 int dash2 = name.indexOf('-', dash1 + 1);
277 int dash3 = name.indexOf('-', dash2 + 1);
278 int dash4 = name.indexOf('-', dash3 + 1);
279 int dash5 = name.indexOf('-', dash4 + 1);
280
281 // For any valid input, dash1 through dash4 will be positive and dash5
282 // negative, but it's enough to check dash4 and dash5:
283 // - if dash1 is -1, dash4 will be -1
284 // - if dash1 is positive but dash2 is -1, dash4 will be -1
285 // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be
286 // positive, but so will dash5
287 if (dash4 < 0 || dash5 >= 0) {
288 throw new IllegalArgumentException("Invalid UUID string: " + name);
289 }
290
291 long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL;
292 mostSigBits <<= 16;
293 mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL;
294 mostSigBits <<= 16;
295 mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL;
296 long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL;
297 leastSigBits <<= 48;
298 leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL;
299
300 return new UUID(mostSigBits, leastSigBits);
301 }
302
303 // Field Accessor Methods
304
305 /**
306 * Returns the least significant 64 bits of this UUID's 128 bit value.
307 *
308 * @return The least significant 64 bits of this UUID's 128 bit value
309 */
310 public long getLeastSignificantBits() {
311 return leastSigBits;
312 }
313
314 /**
315 * Returns the most significant 64 bits of this UUID's 128 bit value.
316 *
317 * @return The most significant 64 bits of this UUID's 128 bit value
318 */
319 public long getMostSignificantBits() {
320 return mostSigBits;
321 }
322
323 /**
324 * The version number associated with this {@code UUID}. The version
325 * number describes how this {@code UUID} was generated.
326 *
327 * The version number has the following meaning:
328 * <ul>
329 * <li>1 Time-based UUID
330 * <li>2 DCE security UUID
331 * <li>3 Name-based UUID
332 * <li>4 Randomly generated UUID
333 * </ul>
334 *
335 * @return The version number of this {@code UUID}
336 */
337 public int version() {
338 // Version is bits masked by 0x000000000000F000 in MS long
339 return (int)((mostSigBits >> 12) & 0x0f);
340 }
341
342 /**
343 * The variant number associated with this {@code UUID}. The variant
344 * number describes the layout of the {@code UUID}.
345 *
346 * The variant number has the following meaning:
347 * <ul>
348 * <li>0 Reserved for NCS backward compatibility
349 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a>
350 * (Leach-Salz), used by this class
351 * <li>6 Reserved, Microsoft Corporation backward compatibility
352 * <li>7 Reserved for future definition
353 * </ul>
354 *
355 * @return The variant number of this {@code UUID}
356 */
357 public int variant() {
358 // This field is composed of a varying number of bits.
359 // 0 - - Reserved for NCS backward compatibility
360 // 1 0 - The IETF aka Leach-Salz variant (used by this class)
361 // 1 1 0 Reserved, Microsoft backward compatibility
362 // 1 1 1 Reserved for future definition.
363 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
364 & (leastSigBits >> 63));
365 }
366
367 /**
368 * The timestamp value associated with this UUID.
369 *
370 * <p> The 60 bit timestamp value is constructed from the time_low,
371 * time_mid, and time_hi fields of this {@code UUID}. The resulting
372 * timestamp is measured in 100-nanosecond units since midnight,
373 * October 15, 1582 UTC.
374 *
375 * <p> The timestamp value is only meaningful in a time-based UUID, which
376 * has version type 1. If this {@code UUID} is not a time-based UUID then
377 * this method throws UnsupportedOperationException.
378 *
379 * @throws UnsupportedOperationException
380 * If this UUID is not a version 1 UUID
381 * @return The timestamp of this {@code UUID}.
382 */
383 public long timestamp() {
384 if (version() != 1) {
385 throw new UnsupportedOperationException("Not a time-based UUID");
386 }
387
388 return (mostSigBits & 0x0FFFL) << 48
389 | ((mostSigBits >> 16) & 0x0FFFFL) << 32
390 | mostSigBits >>> 32;
391 }
392
393 /**
394 * The clock sequence value associated with this UUID.
395 *
396 * <p> The 14 bit clock sequence value is constructed from the clock
397 * sequence field of this UUID. The clock sequence field is used to
398 * guarantee temporal uniqueness in a time-based UUID.
399 *
400 * <p> The {@code clockSequence} value is only meaningful in a time-based
401 * UUID, which has version type 1. If this UUID is not a time-based UUID
402 * then this method throws UnsupportedOperationException.
403 *
404 * @return The clock sequence of this {@code UUID}
405 *
406 * @throws UnsupportedOperationException
407 * If this UUID is not a version 1 UUID
408 */
409 public int clockSequence() {
410 if (version() != 1) {
411 throw new UnsupportedOperationException("Not a time-based UUID");
412 }
413
414 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
415 }
416
417 /**
418 * The node value associated with this UUID.
419 *
420 * <p> The 48 bit node value is constructed from the node field of this
421 * UUID. This field is intended to hold the IEEE 802 address of the machine
422 * that generated this UUID to guarantee spatial uniqueness.
423 *
424 * <p> The node value is only meaningful in a time-based UUID, which has
425 * version type 1. If this UUID is not a time-based UUID then this method
426 * throws UnsupportedOperationException.
427 *
428 * @return The node value of this {@code UUID}
429 *
430 * @throws UnsupportedOperationException
431 * If this UUID is not a version 1 UUID
432 */
433 public long node() {
434 if (version() != 1) {
435 throw new UnsupportedOperationException("Not a time-based UUID");
436 }
437
438 return leastSigBits & 0x0000FFFFFFFFFFFFL;
439 }
440
441 // Object Inherited Methods
442
443 /**
444 * Returns a {@code String} object representing this {@code UUID}.
445 *
446 * <p> The UUID string representation is as described by this BNF:
447 * <blockquote><pre>
448 * {@code
449 * UUID = <time_low> "-" <time_mid> "-"
450 * <time_high_and_version> "-"
451 * <variant_and_sequence> "-"
452 * <node>
453 * time_low = 4*<hexOctet>
454 * time_mid = 2*<hexOctet>
455 * time_high_and_version = 2*<hexOctet>
456 * variant_and_sequence = 2*<hexOctet>
457 * node = 6*<hexOctet>
458 * hexOctet = <hexDigit><hexDigit>
459 * hexDigit =
460 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
461 * | "a" | "b" | "c" | "d" | "e" | "f"
462 * | "A" | "B" | "C" | "D" | "E" | "F"
463 * }</pre></blockquote>
464 *
465 * @return A string representation of this {@code UUID}
466 */
467 public String toString() {
468 return jla.fastUUID(leastSigBits, mostSigBits);
469 }
470
471 /**
472 * Returns a hash code for this {@code UUID}.
473 *
474 * @return A hash code value for this {@code UUID}
475 */
476 public int hashCode() {
477 long hilo = mostSigBits ^ leastSigBits;
478 return ((int)(hilo >> 32)) ^ (int) hilo;
479 }
480
481 /**
482 * Compares this object to the specified object. The result is {@code
483 * true} if and only if the argument is not {@code null}, is a {@code UUID}
484 * object, has the same variant, and contains the same value, bit for bit,
485 * as this {@code UUID}.
486 *
487 * @param obj
488 * The object to be compared
489 *
490 * @return {@code true} if the objects are the same; {@code false}
491 * otherwise
492 */
493 public boolean equals(Object obj) {
494 if ((null == obj) || (obj.getClass() != UUID.class))
495 return false;
496 UUID id = (UUID)obj;
497 return (mostSigBits == id.mostSigBits &&
498 leastSigBits == id.leastSigBits);
499 }
500
501 // Comparison Operations
502
503 /**
504 * Compares this UUID with the specified UUID.
505 *
506 * <p> The first of two UUIDs is greater than the second if the most
507 * significant field in which the UUIDs differ is greater for the first
508 * UUID.
509 *
510 * @param val
511 * {@code UUID} to which this {@code UUID} is to be compared
512 *
513 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or
514 * greater than {@code val}
515 *
516 */
517 public int compareTo(UUID val) {
518 // The ordering is intentionally set up so that the UUIDs
519 // can simply be numerically compared as two numbers
520 return (this.mostSigBits < val.mostSigBits ? -1 :
521 (this.mostSigBits > val.mostSigBits ? 1 :
522 (this.leastSigBits < val.leastSigBits ? -1 :
523 (this.leastSigBits > val.leastSigBits ? 1 :
524 0))));
525 }
526 }