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 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 dash1 = name.indexOf('-', 0);
198 int dash2 = name.indexOf('-', dash1 + 1);
199 int dash3 = name.indexOf('-', dash2 + 1);
200 int dash4 = name.indexOf('-', dash3 + 1);
201 int dash5 = name.indexOf('-', dash4 + 1);
202
203 // For any valid input, dash1 through dash4 will be positive and dash5
204 // negative, but it's enough to check dash4 and dash5:
205 // - if dash1 is -1, dash4 will be -1
206 // - if dash1 is positive but dash2 is -1, dash4 will be -1
207 // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be
208 // positive, but so will dash5
209
210 if (dash4 > 0 && dash5 < 0) {
211 long x1 = Long.parseLong(name, 0, dash1, 16);
212 long x2 = Long.parseLong(name, dash1 + 1, dash2, 16);
213 long x3 = Long.parseLong(name, dash2 + 1, dash3, 16);
214 long x4 = Long.parseLong(name, dash3 + 1, dash4, 16);
215 long x5 = Long.parseLong(name, dash4 + 1, name.length(), 16);
216
217 if (((x1 >> 32) | ((x2 | x3 | x4) >> 16) | (x5 >> 48)) == 0L) {
218 return new UUID((x1 << 32) | (x2 << 16) | x3, (x4 << 48) | x5);
219 }
220 }
221 throw new IllegalArgumentException("Invalid UUID string: " + name);
222 }
223
224 // Field Accessor Methods
225
226 /**
227 * Returns the least significant 64 bits of this UUID's 128 bit value.
228 *
229 * @return The least significant 64 bits of this UUID's 128 bit value
230 */
231 public long getLeastSignificantBits() {
232 return leastSigBits;
233 }
234
235 /**
236 * Returns the most significant 64 bits of this UUID's 128 bit value.
237 *
238 * @return The most significant 64 bits of this UUID's 128 bit value
239 */
240 public long getMostSignificantBits() {
241 return mostSigBits;
242 }
243
244 /**
245 * The version number associated with this {@code UUID}. The version
246 * number describes how this {@code UUID} was generated.
247 *
248 * The version number has the following meaning:
249 * <ul>
250 * <li>1 Time-based UUID
251 * <li>2 DCE security UUID
252 * <li>3 Name-based UUID
253 * <li>4 Randomly generated UUID
254 * </ul>
255 *
256 * @return The version number of this {@code UUID}
257 */
258 public int version() {
259 // Version is bits masked by 0x000000000000F000 in MS long
260 return (int)((mostSigBits >> 12) & 0x0f);
261 }
262
263 /**
264 * The variant number associated with this {@code UUID}. The variant
265 * number describes the layout of the {@code UUID}.
266 *
267 * The variant number has the following meaning:
268 * <ul>
269 * <li>0 Reserved for NCS backward compatibility
270 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a>
271 * (Leach-Salz), used by this class
272 * <li>6 Reserved, Microsoft Corporation backward compatibility
273 * <li>7 Reserved for future definition
274 * </ul>
275 *
276 * @return The variant number of this {@code UUID}
277 */
278 public int variant() {
279 // This field is composed of a varying number of bits.
280 // 0 - - Reserved for NCS backward compatibility
281 // 1 0 - The IETF aka Leach-Salz variant (used by this class)
282 // 1 1 0 Reserved, Microsoft backward compatibility
283 // 1 1 1 Reserved for future definition.
284 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
285 & (leastSigBits >> 63));
286 }
287
288 /**
289 * The timestamp value associated with this UUID.
290 *
291 * <p> The 60 bit timestamp value is constructed from the time_low,
292 * time_mid, and time_hi fields of this {@code UUID}. The resulting
293 * timestamp is measured in 100-nanosecond units since midnight,
294 * October 15, 1582 UTC.
295 *
296 * <p> The timestamp value is only meaningful in a time-based UUID, which
297 * has version type 1. If this {@code UUID} is not a time-based UUID then
298 * this method throws UnsupportedOperationException.
299 *
300 * @throws UnsupportedOperationException
301 * If this UUID is not a version 1 UUID
302 * @return The timestamp of this {@code UUID}.
303 */
304 public long timestamp() {
305 if (version() != 1) {
306 throw new UnsupportedOperationException("Not a time-based UUID");
307 }
308
309 return (mostSigBits & 0x0FFFL) << 48
310 | ((mostSigBits >> 16) & 0x0FFFFL) << 32
311 | mostSigBits >>> 32;
312 }
313
314 /**
315 * The clock sequence value associated with this UUID.
316 *
317 * <p> The 14 bit clock sequence value is constructed from the clock
318 * sequence field of this UUID. The clock sequence field is used to
319 * guarantee temporal uniqueness in a time-based UUID.
320 *
321 * <p> The {@code clockSequence} value is only meaningful in a time-based
322 * UUID, which has version type 1. If this UUID is not a time-based UUID
323 * then this method throws UnsupportedOperationException.
324 *
325 * @return The clock sequence of this {@code UUID}
326 *
327 * @throws UnsupportedOperationException
328 * If this UUID is not a version 1 UUID
329 */
330 public int clockSequence() {
331 if (version() != 1) {
332 throw new UnsupportedOperationException("Not a time-based UUID");
333 }
334
335 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
336 }
337
338 /**
339 * The node value associated with this UUID.
340 *
341 * <p> The 48 bit node value is constructed from the node field of this
342 * UUID. This field is intended to hold the IEEE 802 address of the machine
343 * that generated this UUID to guarantee spatial uniqueness.
344 *
345 * <p> The node value is only meaningful in a time-based UUID, which has
346 * version type 1. If this UUID is not a time-based UUID then this method
347 * throws UnsupportedOperationException.
348 *
349 * @return The node value of this {@code UUID}
350 *
351 * @throws UnsupportedOperationException
352 * If this UUID is not a version 1 UUID
353 */
354 public long node() {
355 if (version() != 1) {
356 throw new UnsupportedOperationException("Not a time-based UUID");
357 }
358
359 return leastSigBits & 0x0000FFFFFFFFFFFFL;
360 }
361
362 // Object Inherited Methods
363
364 /**
365 * Returns a {@code String} object representing this {@code UUID}.
366 *
367 * <p> The UUID string representation is as described by this BNF:
368 * <blockquote><pre>
369 * {@code
370 * UUID = <time_low> "-" <time_mid> "-"
371 * <time_high_and_version> "-"
372 * <variant_and_sequence> "-"
373 * <node>
374 * time_low = 4*<hexOctet>
375 * time_mid = 2*<hexOctet>
376 * time_high_and_version = 2*<hexOctet>
377 * variant_and_sequence = 2*<hexOctet>
378 * node = 6*<hexOctet>
379 * hexOctet = <hexDigit><hexDigit>
380 * hexDigit =
381 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
382 * | "a" | "b" | "c" | "d" | "e" | "f"
383 * | "A" | "B" | "C" | "D" | "E" | "F"
384 * }</pre></blockquote>
385 *
386 * @return A string representation of this {@code UUID}
387 */
388 public String toString() {
389 return jla.fastUUID(leastSigBits, mostSigBits);
390 }
391
392 /**
393 * Returns a hash code for this {@code UUID}.
394 *
395 * @return A hash code value for this {@code UUID}
396 */
397 public int hashCode() {
398 long hilo = mostSigBits ^ leastSigBits;
399 return ((int)(hilo >> 32)) ^ (int) hilo;
400 }
401
402 /**
403 * Compares this object to the specified object. The result is {@code
404 * true} if and only if the argument is not {@code null}, is a {@code UUID}
405 * object, has the same variant, and contains the same value, bit for bit,
406 * as this {@code UUID}.
407 *
408 * @param obj
409 * The object to be compared
410 *
411 * @return {@code true} if the objects are the same; {@code false}
412 * otherwise
413 */
414 public boolean equals(Object obj) {
415 if ((null == obj) || (obj.getClass() != UUID.class))
416 return false;
417 UUID id = (UUID)obj;
418 return (mostSigBits == id.mostSigBits &&
419 leastSigBits == id.leastSigBits);
420 }
421
422 // Comparison Operations
423
424 /**
425 * Compares this UUID with the specified UUID.
426 *
427 * <p> The first of two UUIDs is greater than the second if the most
428 * significant field in which the UUIDs differ is greater for the first
429 * UUID.
430 *
431 * @param val
432 * {@code UUID} to which this {@code UUID} is to be compared
433 *
434 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or
435 * greater than {@code val}
436 *
437 */
438 public int compareTo(UUID val) {
439 // The ordering is intentionally set up so that the UUIDs
440 // can simply be numerically compared as two numbers
441 return (this.mostSigBits < val.mostSigBits ? -1 :
442 (this.mostSigBits > val.mostSigBits ? 1 :
443 (this.leastSigBits < val.leastSigBits ? -1 :
444 (this.leastSigBits > val.leastSigBits ? 1 :
445 0))));
446 }
447 }