1 /*
2 * Copyright (c) 2003, 2014, 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 len = name.length();
198 if (len > 36) {
199 throw new IllegalArgumentException("UUID string too large");
200 }
201
202 int dash1 = name.indexOf('-', 0);
203 int dash2 = name.indexOf('-', dash1 + 1);
204 int dash3 = name.indexOf('-', dash2 + 1);
205 int dash4 = name.indexOf('-', dash3 + 1);
206 int dash5 = name.indexOf('-', dash4 + 1);
207
208 // For any valid input, dash1 through dash4 will be positive and dash5
209 // negative, but it's enough to check dash4 and dash5:
210 // - if dash1 is -1, dash4 will be -1
211 // - if dash1 is positive but dash2 is -1, dash4 will be -1
212 // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be
213 // positive, but so will dash5
214 if (dash4 < 0 || dash5 >= 0) {
215 throw new IllegalArgumentException("Invalid UUID string: " + name);
216 }
217
218 long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL;
219 mostSigBits <<= 16;
220 mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL;
221 mostSigBits <<= 16;
222 mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL;
223 long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL;
224 leastSigBits <<= 48;
225 leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL;
226
227 return new UUID(mostSigBits, leastSigBits);
228 }
229
230 // Field Accessor Methods
231
232 /**
233 * Returns the least significant 64 bits of this UUID's 128 bit value.
234 *
235 * @return The least significant 64 bits of this UUID's 128 bit value
236 */
237 public long getLeastSignificantBits() {
238 return leastSigBits;
239 }
240
241 /**
242 * Returns the most significant 64 bits of this UUID's 128 bit value.
243 *
244 * @return The most significant 64 bits of this UUID's 128 bit value
245 */
246 public long getMostSignificantBits() {
247 return mostSigBits;
248 }
249
250 /**
251 * The version number associated with this {@code UUID}. The version
252 * number describes how this {@code UUID} was generated.
253 *
254 * The version number has the following meaning:
255 * <ul>
256 * <li>1 Time-based UUID
257 * <li>2 DCE security UUID
258 * <li>3 Name-based UUID
259 * <li>4 Randomly generated UUID
260 * </ul>
261 *
262 * @return The version number of this {@code UUID}
263 */
264 public int version() {
265 // Version is bits masked by 0x000000000000F000 in MS long
266 return (int)((mostSigBits >> 12) & 0x0f);
267 }
268
269 /**
270 * The variant number associated with this {@code UUID}. The variant
271 * number describes the layout of the {@code UUID}.
272 *
273 * The variant number has the following meaning:
274 * <ul>
275 * <li>0 Reserved for NCS backward compatibility
276 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a>
277 * (Leach-Salz), used by this class
278 * <li>6 Reserved, Microsoft Corporation backward compatibility
279 * <li>7 Reserved for future definition
280 * </ul>
281 *
282 * @return The variant number of this {@code UUID}
283 */
284 public int variant() {
285 // This field is composed of a varying number of bits.
286 // 0 - - Reserved for NCS backward compatibility
287 // 1 0 - The IETF aka Leach-Salz variant (used by this class)
288 // 1 1 0 Reserved, Microsoft backward compatibility
289 // 1 1 1 Reserved for future definition.
290 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
291 & (leastSigBits >> 63));
292 }
293
294 /**
295 * The timestamp value associated with this UUID.
296 *
297 * <p> The 60 bit timestamp value is constructed from the time_low,
298 * time_mid, and time_hi fields of this {@code UUID}. The resulting
299 * timestamp is measured in 100-nanosecond units since midnight,
300 * October 15, 1582 UTC.
301 *
302 * <p> The timestamp value is only meaningful in a time-based UUID, which
303 * has version type 1. If this {@code UUID} is not a time-based UUID then
304 * this method throws UnsupportedOperationException.
305 *
306 * @throws UnsupportedOperationException
307 * If this UUID is not a version 1 UUID
308 * @return The timestamp of this {@code UUID}.
309 */
310 public long timestamp() {
311 if (version() != 1) {
312 throw new UnsupportedOperationException("Not a time-based UUID");
313 }
314
315 return (mostSigBits & 0x0FFFL) << 48
316 | ((mostSigBits >> 16) & 0x0FFFFL) << 32
317 | mostSigBits >>> 32;
318 }
319
320 /**
321 * The clock sequence value associated with this UUID.
322 *
323 * <p> The 14 bit clock sequence value is constructed from the clock
324 * sequence field of this UUID. The clock sequence field is used to
325 * guarantee temporal uniqueness in a time-based UUID.
326 *
327 * <p> The {@code clockSequence} value is only meaningful in a time-based
328 * UUID, which has version type 1. If this UUID is not a time-based UUID
329 * then this method throws UnsupportedOperationException.
330 *
331 * @return The clock sequence of this {@code UUID}
332 *
333 * @throws UnsupportedOperationException
334 * If this UUID is not a version 1 UUID
335 */
336 public int clockSequence() {
337 if (version() != 1) {
338 throw new UnsupportedOperationException("Not a time-based UUID");
339 }
340
341 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
342 }
343
344 /**
345 * The node value associated with this UUID.
346 *
347 * <p> The 48 bit node value is constructed from the node field of this
348 * UUID. This field is intended to hold the IEEE 802 address of the machine
349 * that generated this UUID to guarantee spatial uniqueness.
350 *
351 * <p> The node value is only meaningful in a time-based UUID, which has
352 * version type 1. If this UUID is not a time-based UUID then this method
353 * throws UnsupportedOperationException.
354 *
355 * @return The node value of this {@code UUID}
356 *
357 * @throws UnsupportedOperationException
358 * If this UUID is not a version 1 UUID
359 */
360 public long node() {
361 if (version() != 1) {
362 throw new UnsupportedOperationException("Not a time-based UUID");
363 }
364
365 return leastSigBits & 0x0000FFFFFFFFFFFFL;
366 }
367
368 // Object Inherited Methods
369
370 /**
371 * Returns a {@code String} object representing this {@code UUID}.
372 *
373 * <p> The UUID string representation is as described by this BNF:
374 * <blockquote><pre>
375 * {@code
376 * UUID = <time_low> "-" <time_mid> "-"
377 * <time_high_and_version> "-"
378 * <variant_and_sequence> "-"
379 * <node>
380 * time_low = 4*<hexOctet>
381 * time_mid = 2*<hexOctet>
382 * time_high_and_version = 2*<hexOctet>
383 * variant_and_sequence = 2*<hexOctet>
384 * node = 6*<hexOctet>
385 * hexOctet = <hexDigit><hexDigit>
386 * hexDigit =
387 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
388 * | "a" | "b" | "c" | "d" | "e" | "f"
389 * | "A" | "B" | "C" | "D" | "E" | "F"
390 * }</pre></blockquote>
391 *
392 * @return A string representation of this {@code UUID}
393 */
394 public String toString() {
395 return jla.fastUUID(leastSigBits, mostSigBits);
396 }
397
398 /**
399 * Returns a hash code for this {@code UUID}.
400 *
401 * @return A hash code value for this {@code UUID}
402 */
403 public int hashCode() {
404 long hilo = mostSigBits ^ leastSigBits;
405 return ((int)(hilo >> 32)) ^ (int) hilo;
406 }
407
408 /**
409 * Compares this object to the specified object. The result is {@code
410 * true} if and only if the argument is not {@code null}, is a {@code UUID}
411 * object, has the same variant, and contains the same value, bit for bit,
412 * as this {@code UUID}.
413 *
414 * @param obj
415 * The object to be compared
416 *
417 * @return {@code true} if the objects are the same; {@code false}
418 * otherwise
419 */
420 public boolean equals(Object obj) {
421 if ((null == obj) || (obj.getClass() != UUID.class))
422 return false;
423 UUID id = (UUID)obj;
424 return (mostSigBits == id.mostSigBits &&
425 leastSigBits == id.leastSigBits);
426 }
427
428 // Comparison Operations
429
430 /**
431 * Compares this UUID with the specified UUID.
432 *
433 * <p> The first of two UUIDs is greater than the second if the most
434 * significant field in which the UUIDs differ is greater for the first
435 * UUID.
436 *
437 * @param val
438 * {@code UUID} to which this {@code UUID} is to be compared
439 *
440 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or
441 * greater than {@code val}
442 *
443 */
444 public int compareTo(UUID val) {
445 // The ordering is intentionally set up so that the UUIDs
446 // can simply be numerically compared as two numbers
447 return (this.mostSigBits < val.mostSigBits ? -1 :
448 (this.mostSigBits > val.mostSigBits ? 1 :
449 (this.leastSigBits < val.leastSigBits ? -1 :
450 (this.leastSigBits > val.leastSigBits ? 1 :
451 0))));
452 }
453 }