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 * Creates a {@code UUID} from the string standard representation as
185 * described in the {@link #toString} method.
186 *
187 * @param name
188 * A string that specifies a {@code UUID}
189 *
190 * @return A {@code UUID} with the specified value
191 *
192 * @throws IllegalArgumentException
193 * If name does not conform to the string representation as
194 * described in {@link #toString}
195 *
196 */
197 public static UUID fromString(String name) {
198 int len = name.length();
199 if (len > 36) {
200 throw new IllegalArgumentException("UUID string too large");
201 }
202
203 int dash1 = name.indexOf('-', 0);
204 int dash2 = name.indexOf('-', dash1 + 1);
205 int dash3 = name.indexOf('-', dash2 + 1);
206 int dash4 = name.indexOf('-', dash3 + 1);
207 int dash5 = name.indexOf('-', dash4 + 1);
208
209 int len1 = dash1;
210 int len2 = dash2 - dash1 - 1;
211 int len3 = dash3 - dash2 - 1;
212 int len4 = dash4 - dash3 - 1;
213 int len5 = len - dash4 - 1;
214
215 if (len1 > 8 || len2 > 4 || len3 > 4 || len4 > 4 || len5 > 12) {
216 throw new IllegalArgumentException("Invalid UUID string: " + name);
217 }
218
219 // For any valid input, dash1 through dash4 will be positive and dash5
220 // negative, but it's enough to check dash4 and dash5:
221 // - if dash1 is -1, dash4 will be -1
222 // - if dash1 is positive but dash2 is -1, dash4 will be -1
223 // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be
224 // positive, but so will dash5
225 if (dash4 < 0 || dash5 >= 0) {
226 throw new IllegalArgumentException("Invalid UUID string: " + name);
227 }
228
229 long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL;
230 mostSigBits <<= 16;
231 mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL;
232 mostSigBits <<= 16;
233 mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL;
234 long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL;
235 leastSigBits <<= 48;
236 leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL;
237
238 return new UUID(mostSigBits, leastSigBits);
239 }
240
241 // Field Accessor Methods
242
243 /**
244 * Returns the least significant 64 bits of this UUID's 128 bit value.
245 *
246 * @return The least significant 64 bits of this UUID's 128 bit value
247 */
248 public long getLeastSignificantBits() {
249 return leastSigBits;
250 }
251
252 /**
253 * Returns the most significant 64 bits of this UUID's 128 bit value.
254 *
255 * @return The most significant 64 bits of this UUID's 128 bit value
256 */
257 public long getMostSignificantBits() {
258 return mostSigBits;
259 }
260
261 /**
262 * The version number associated with this {@code UUID}. The version
263 * number describes how this {@code UUID} was generated.
264 *
265 * The version number has the following meaning:
266 * <ul>
267 * <li>1 Time-based UUID
268 * <li>2 DCE security UUID
269 * <li>3 Name-based UUID
270 * <li>4 Randomly generated UUID
271 * </ul>
272 *
273 * @return The version number of this {@code UUID}
274 */
275 public int version() {
276 // Version is bits masked by 0x000000000000F000 in MS long
277 return (int)((mostSigBits >> 12) & 0x0f);
278 }
279
280 /**
281 * The variant number associated with this {@code UUID}. The variant
282 * number describes the layout of the {@code UUID}.
283 *
284 * The variant number has the following meaning:
285 * <ul>
286 * <li>0 Reserved for NCS backward compatibility
287 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a>
288 * (Leach-Salz), used by this class
289 * <li>6 Reserved, Microsoft Corporation backward compatibility
290 * <li>7 Reserved for future definition
291 * </ul>
292 *
293 * @return The variant number of this {@code UUID}
294 */
295 public int variant() {
296 // This field is composed of a varying number of bits.
297 // 0 - - Reserved for NCS backward compatibility
298 // 1 0 - The IETF aka Leach-Salz variant (used by this class)
299 // 1 1 0 Reserved, Microsoft backward compatibility
300 // 1 1 1 Reserved for future definition.
301 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
302 & (leastSigBits >> 63));
303 }
304
305 /**
306 * The timestamp value associated with this UUID.
307 *
308 * <p> The 60 bit timestamp value is constructed from the time_low,
309 * time_mid, and time_hi fields of this {@code UUID}. The resulting
310 * timestamp is measured in 100-nanosecond units since midnight,
311 * October 15, 1582 UTC.
312 *
313 * <p> The timestamp value is only meaningful in a time-based UUID, which
314 * has version type 1. If this {@code UUID} is not a time-based UUID then
315 * this method throws UnsupportedOperationException.
316 *
317 * @throws UnsupportedOperationException
318 * If this UUID is not a version 1 UUID
319 * @return The timestamp of this {@code UUID}.
320 */
321 public long timestamp() {
322 if (version() != 1) {
323 throw new UnsupportedOperationException("Not a time-based UUID");
324 }
325
326 return (mostSigBits & 0x0FFFL) << 48
327 | ((mostSigBits >> 16) & 0x0FFFFL) << 32
328 | mostSigBits >>> 32;
329 }
330
331 /**
332 * The clock sequence value associated with this UUID.
333 *
334 * <p> The 14 bit clock sequence value is constructed from the clock
335 * sequence field of this UUID. The clock sequence field is used to
336 * guarantee temporal uniqueness in a time-based UUID.
337 *
338 * <p> The {@code clockSequence} value is only meaningful in a time-based
339 * UUID, which has version type 1. If this UUID is not a time-based UUID
340 * then this method throws UnsupportedOperationException.
341 *
342 * @return The clock sequence of this {@code UUID}
343 *
344 * @throws UnsupportedOperationException
345 * If this UUID is not a version 1 UUID
346 */
347 public int clockSequence() {
348 if (version() != 1) {
349 throw new UnsupportedOperationException("Not a time-based UUID");
350 }
351
352 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
353 }
354
355 /**
356 * The node value associated with this UUID.
357 *
358 * <p> The 48 bit node value is constructed from the node field of this
359 * UUID. This field is intended to hold the IEEE 802 address of the machine
360 * that generated this UUID to guarantee spatial uniqueness.
361 *
362 * <p> The node value is only meaningful in a time-based UUID, which has
363 * version type 1. If this UUID is not a time-based UUID then this method
364 * throws UnsupportedOperationException.
365 *
366 * @return The node value of this {@code UUID}
367 *
368 * @throws UnsupportedOperationException
369 * If this UUID is not a version 1 UUID
370 */
371 public long node() {
372 if (version() != 1) {
373 throw new UnsupportedOperationException("Not a time-based UUID");
374 }
375
376 return leastSigBits & 0x0000FFFFFFFFFFFFL;
377 }
378
379 // Object Inherited Methods
380
381 /**
382 * Returns a {@code String} object representing this {@code UUID}.
383 *
384 * <p> The UUID string representation is as described by this BNF:
385 * <blockquote><pre>
386 * {@code
387 * UUID = <time_low> "-" <time_mid> "-"
388 * <time_high_and_version> "-"
389 * <variant_and_sequence> "-"
390 * <node>
391 * time_low = 4*<hexOctet>
392 * time_mid = 2*<hexOctet>
393 * time_high_and_version = 2*<hexOctet>
394 * variant_and_sequence = 2*<hexOctet>
395 * node = 6*<hexOctet>
396 * hexOctet = <hexDigit><hexDigit>
397 * hexDigit =
398 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
399 * | "a" | "b" | "c" | "d" | "e" | "f"
400 * | "A" | "B" | "C" | "D" | "E" | "F"
401 * }</pre></blockquote>
402 *
403 * @return A string representation of this {@code UUID}
404 */
405 public String toString() {
406 return jla.fastUUID(leastSigBits, mostSigBits);
407 }
408
409 /**
410 * Returns a hash code for this {@code UUID}.
411 *
412 * @return A hash code value for this {@code UUID}
413 */
414 public int hashCode() {
415 long hilo = mostSigBits ^ leastSigBits;
416 return ((int)(hilo >> 32)) ^ (int) hilo;
417 }
418
419 /**
420 * Compares this object to the specified object. The result is {@code
421 * true} if and only if the argument is not {@code null}, is a {@code UUID}
422 * object, has the same variant, and contains the same value, bit for bit,
423 * as this {@code UUID}.
424 *
425 * @param obj
426 * The object to be compared
427 *
428 * @return {@code true} if the objects are the same; {@code false}
429 * otherwise
430 */
431 public boolean equals(Object obj) {
432 if ((null == obj) || (obj.getClass() != UUID.class))
433 return false;
434 UUID id = (UUID)obj;
435 return (mostSigBits == id.mostSigBits &&
436 leastSigBits == id.leastSigBits);
437 }
438
439 // Comparison Operations
440
441 /**
442 * Compares this UUID with the specified UUID.
443 *
444 * <p> The first of two UUIDs is greater than the second if the most
445 * significant field in which the UUIDs differ is greater for the first
446 * UUID.
447 *
448 * @param val
449 * {@code UUID} to which this {@code UUID} is to be compared
450 *
451 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or
452 * greater than {@code val}
453 *
454 */
455 public int compareTo(UUID val) {
456 // The ordering is intentionally set up so that the UUIDs
457 // can simply be numerically compared as two numbers
458 return (this.mostSigBits < val.mostSigBits ? -1 :
459 (this.mostSigBits > val.mostSigBits ? 1 :
460 (this.leastSigBits < val.leastSigBits ? -1 :
461 (this.leastSigBits > val.leastSigBits ? 1 :
462 0))));
463 }
464 }