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