1 /*
2 * Copyright (c) 2003, 2013, 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 sun.misc.JavaLangAccess;
31 import sun.misc.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
202 if (name.indexOf('-', dash4 + 1) > 0) {
203 throw new IllegalArgumentException("Invalid UUID string: " + name);
204 }
205
206 long mostSigBits = Long.parseLong(name, 16, 0, dash1) & 0xffffffffL;
207 mostSigBits <<= 16;
208 mostSigBits |= Long.parseLong(name, 16, dash1 + 1, dash2) & 0xffffL;
209 mostSigBits <<= 16;
210 mostSigBits |= Long.parseLong(name, 16, dash2 + 1, dash3) & 0xffffL;
211
212 long leastSigBits = Long.parseLong(name, 16, dash3 + 1, dash4) & 0xffffL;
213 leastSigBits <<= 48;
214 leastSigBits |= Long.parseLong(name, 16, dash4 + 1) & 0xffffffffffffL;
215
216 return new UUID(mostSigBits, leastSigBits);
217 }
218
219 // Field Accessor Methods
220
221 /**
222 * Returns the least significant 64 bits of this UUID's 128 bit value.
223 *
224 * @return The least significant 64 bits of this UUID's 128 bit value
225 */
226 public long getLeastSignificantBits() {
227 return leastSigBits;
228 }
229
230 /**
231 * Returns the most significant 64 bits of this UUID's 128 bit value.
232 *
233 * @return The most significant 64 bits of this UUID's 128 bit value
234 */
235 public long getMostSignificantBits() {
236 return mostSigBits;
237 }
238
239 /**
240 * The version number associated with this {@code UUID}. The version
241 * number describes how this {@code UUID} was generated.
242 *
243 * The version number has the following meaning:
244 * <ul>
245 * <li>1 Time-based UUID
246 * <li>2 DCE security UUID
247 * <li>3 Name-based UUID
248 * <li>4 Randomly generated UUID
249 * </ul>
250 *
251 * @return The version number of this {@code UUID}
252 */
253 public int version() {
254 // Version is bits masked by 0x000000000000F000 in MS long
255 return (int)((mostSigBits >> 12) & 0x0f);
256 }
257
258 /**
259 * The variant number associated with this {@code UUID}. The variant
260 * number describes the layout of the {@code UUID}.
261 *
262 * The variant number has the following meaning:
263 * <ul>
264 * <li>0 Reserved for NCS backward compatibility
265 * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a>
266 * (Leach-Salz), used by this class
267 * <li>6 Reserved, Microsoft Corporation backward compatibility
268 * <li>7 Reserved for future definition
269 * </ul>
270 *
271 * @return The variant number of this {@code UUID}
272 */
273 public int variant() {
274 // This field is composed of a varying number of bits.
275 // 0 - - Reserved for NCS backward compatibility
276 // 1 0 - The IETF aka Leach-Salz variant (used by this class)
277 // 1 1 0 Reserved, Microsoft backward compatibility
278 // 1 1 1 Reserved for future definition.
279 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
280 & (leastSigBits >> 63));
281 }
282
283 /**
284 * The timestamp value associated with this UUID.
285 *
286 * <p> The 60 bit timestamp value is constructed from the time_low,
287 * time_mid, and time_hi fields of this {@code UUID}. The resulting
288 * timestamp is measured in 100-nanosecond units since midnight,
289 * October 15, 1582 UTC.
290 *
291 * <p> The timestamp value is only meaningful in a time-based UUID, which
292 * has version type 1. If this {@code UUID} is not a time-based UUID then
293 * this method throws UnsupportedOperationException.
294 *
295 * @throws UnsupportedOperationException
296 * If this UUID is not a version 1 UUID
297 * @return The timestamp of this {@code UUID}.
298 */
299 public long timestamp() {
300 if (version() != 1) {
301 throw new UnsupportedOperationException("Not a time-based UUID");
302 }
303
304 return (mostSigBits & 0x0FFFL) << 48
305 | ((mostSigBits >> 16) & 0x0FFFFL) << 32
306 | mostSigBits >>> 32;
307 }
308
309 /**
310 * The clock sequence value associated with this UUID.
311 *
312 * <p> The 14 bit clock sequence value is constructed from the clock
313 * sequence field of this UUID. The clock sequence field is used to
314 * guarantee temporal uniqueness in a time-based UUID.
315 *
316 * <p> The {@code clockSequence} value is only meaningful in a time-based
317 * UUID, which has version type 1. If this UUID is not a time-based UUID
318 * then this method throws UnsupportedOperationException.
319 *
320 * @return The clock sequence of this {@code UUID}
321 *
322 * @throws UnsupportedOperationException
323 * If this UUID is not a version 1 UUID
324 */
325 public int clockSequence() {
326 if (version() != 1) {
327 throw new UnsupportedOperationException("Not a time-based UUID");
328 }
329
330 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
331 }
332
333 /**
334 * The node value associated with this UUID.
335 *
336 * <p> The 48 bit node value is constructed from the node field of this
337 * UUID. This field is intended to hold the IEEE 802 address of the machine
338 * that generated this UUID to guarantee spatial uniqueness.
339 *
340 * <p> The node value is only meaningful in a time-based UUID, which has
341 * version type 1. If this UUID is not a time-based UUID then this method
342 * throws UnsupportedOperationException.
343 *
344 * @return The node value of this {@code UUID}
345 *
346 * @throws UnsupportedOperationException
347 * If this UUID is not a version 1 UUID
348 */
349 public long node() {
350 if (version() != 1) {
351 throw new UnsupportedOperationException("Not a time-based UUID");
352 }
353
354 return leastSigBits & 0x0000FFFFFFFFFFFFL;
355 }
356
357 // Object Inherited Methods
358
359 /**
360 * Returns a {@code String} object representing this {@code UUID}.
361 *
362 * <p> The UUID string representation is as described by this BNF:
363 * <blockquote><pre>
364 * {@code
365 * UUID = <time_low> "-" <time_mid> "-"
366 * <time_high_and_version> "-"
367 * <variant_and_sequence> "-"
368 * <node>
369 * time_low = 4*<hexOctet>
370 * time_mid = 2*<hexOctet>
371 * time_high_and_version = 2*<hexOctet>
372 * variant_and_sequence = 2*<hexOctet>
373 * node = 6*<hexOctet>
374 * hexOctet = <hexDigit><hexDigit>
375 * hexDigit =
376 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
377 * | "a" | "b" | "c" | "d" | "e" | "f"
378 * | "A" | "B" | "C" | "D" | "E" | "F"
379 * }</pre></blockquote>
380 *
381 * @return A string representation of this {@code UUID}
382 */
383 public String toString() {
384 char[] chars = new char[36];
385 digits(mostSigBits >> 32, chars, 0, 8);
386 chars[8] = '-';
387 digits(mostSigBits >> 16, chars, 9, 4);
388 chars[13] = '-';
389 digits(mostSigBits, chars, 14, 4);
390 chars[18] = '-';
391 digits(leastSigBits >> 48, chars, 19, 4);
392 chars[23] = '-';
393 digits(leastSigBits, chars, 24, 12);
394 return jla.newStringUnsafe(chars);
395 }
396
397 private static void digits(long val, char[] chars, int offset, int len) {
398 jla.formatUnsignedLong(val, 4, chars, offset, len);
399 }
400
401 /**
402 * Returns a hash code for this {@code UUID}.
403 *
404 * @return A hash code value for this {@code UUID}
405 */
406 public int hashCode() {
407 long hilo = mostSigBits ^ leastSigBits;
408 return ((int)(hilo >> 32)) ^ (int) hilo;
409 }
410
411 /**
412 * Compares this object to the specified object. The result is {@code
413 * true} if and only if the argument is not {@code null}, is a {@code UUID}
414 * object, has the same variant, and contains the same value, bit for bit,
415 * as this {@code UUID}.
416 *
417 * @param obj
418 * The object to be compared
419 *
420 * @return {@code true} if the objects are the same; {@code false}
421 * otherwise
422 */
423 public boolean equals(Object obj) {
424 if ((null == obj) || (obj.getClass() != UUID.class))
425 return false;
426 UUID id = (UUID)obj;
427 return (mostSigBits == id.mostSigBits &&
428 leastSigBits == id.leastSigBits);
429 }
430
431 // Comparison Operations
432
433 /**
434 * Compares this UUID with the specified UUID.
435 *
436 * <p> The first of two UUIDs is greater than the second if the most
437 * significant field in which the UUIDs differ is greater for the first
438 * UUID.
439 *
440 * @param val
441 * {@code UUID} to which this {@code UUID} is to be compared
442 *
443 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or
444 * greater than {@code val}
445 *
446 */
447 public int compareTo(UUID val) {
448 // The ordering is intentionally set up so that the UUIDs
449 // can simply be numerically compared as two numbers
450 return (this.mostSigBits < val.mostSigBits ? -1 :
451 (this.mostSigBits > val.mostSigBits ? 1 :
452 (this.leastSigBits < val.leastSigBits ? -1 :
453 (this.leastSigBits > val.leastSigBits ? 1 :
454 0))));
455 }
456 }