1 /*
2 * Copyright (c) 2003, 2011, 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 /**
31 * A class that represents an immutable universally unique identifier (UUID).
32 * A UUID represents a 128-bit value.
33 *
34 * <p> There exist different variants of these global identifiers. The methods
35 * of this class are for manipulating the Leach-Salz variant, although the
36 * constructors allow the creation of any variant of UUID (described below).
37 *
38 * <p> The layout of a variant 2 (Leach-Salz) UUID is as follows:
39 *
40 * The most significant long consists of the following unsigned fields:
41 * <pre>
42 * 0xFFFFFFFF00000000 time_low
43 * 0x00000000FFFF0000 time_mid
44 * 0x000000000000F000 version
45 * 0x0000000000000FFF time_hi
46 * </pre>
47 * The least significant long consists of the following unsigned fields:
48 * <pre>
49 * 0xC000000000000000 variant
50 * 0x3FFF000000000000 clock_seq
51 * 0x0000FFFFFFFFFFFF node
52 * </pre>
53 *
54 * <p> The variant field contains a value which identifies the layout of the
55 * {@code UUID}. The bit layout described above is valid only for a {@code
56 * UUID} with a variant value of 2, which indicates the Leach-Salz variant.
57 *
58 * <p> The version field holds a value that describes the type of this {@code
59 * UUID}. There are four different basic types of UUIDs: time-based, DCE
60 * security, name-based, and randomly generated UUIDs. These types have a
61 * version value of 1, 2, 3 and 4, respectively.
62 *
63 * <p> For more information including algorithms used to create {@code UUID}s,
64 * see <a href="http://www.ietf.org/rfc/rfc4122.txt"> <i>RFC 4122: A
65 * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2
66 * "Algorithms for Creating a Time-Based UUID".
67 *
68 * @since 1.5
69 */
70 public final class UUID implements java.io.Serializable, Comparable<UUID> {
71
72 /**
73 * Explicit serialVersionUID for interoperability.
74 */
75 private static final long serialVersionUID = -4856846361193249489L;
76
77 /*
78 * The most significant 64 bits of this UUID.
79 *
80 * @serial
81 */
82 private final long mostSigBits;
83
84 /*
85 * The least significant 64 bits of this UUID.
86 *
87 * @serial
88 */
89 private final long leastSigBits;
90
91 /*
92 * The random number generator used by this class to create random
93 * based UUIDs. In a holder class to defer initialization until needed.
94 */
95 private static class Holder {
96 static final SecureRandom numberGenerator = new SecureRandom();
97 }
98
99 // Constructors and Factories
100
101 /*
102 * Private constructor which uses a byte array to construct the new UUID.
103 */
104 private UUID(byte[] data) {
105 long msb = 0;
106 long lsb = 0;
107 assert data.length == 16 : "data must be 16 bytes in length";
108 for (int i=0; i<8; i++)
109 msb = (msb << 8) | (data[i] & 0xff);
110 for (int i=8; i<16; i++)
111 lsb = (lsb << 8) | (data[i] & 0xff);
112 this.mostSigBits = msb;
113 this.leastSigBits = lsb;
114 }
115
116 /**
117 * Constructs a new {@code UUID} using the specified data. {@code
118 * mostSigBits} is used for the most significant 64 bits of the {@code
119 * UUID} and {@code leastSigBits} becomes the least significant 64 bits of
120 * the {@code UUID}.
121 *
122 * @param mostSigBits
123 * The most significant bits of the {@code UUID}
124 *
125 * @param leastSigBits
126 * The least significant bits of the {@code UUID}
127 */
128 public UUID(long mostSigBits, long leastSigBits) {
129 this.mostSigBits = mostSigBits;
130 this.leastSigBits = leastSigBits;
131 }
132
133 /**
134 * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
135 *
136 * The {@code UUID} is generated using a cryptographically strong pseudo
137 * random number generator.
138 *
139 * @return A randomly generated {@code UUID}
140 */
141 public static UUID randomUUID() {
142 SecureRandom ng = Holder.numberGenerator;
143
144 byte[] randomBytes = new byte[16];
145 ng.nextBytes(randomBytes);
146 randomBytes[6] &= 0x0f; /* clear version */
147 randomBytes[6] |= 0x40; /* set to version 4 */
148 randomBytes[8] &= 0x3f; /* clear variant */
149 randomBytes[8] |= 0x80; /* set to IETF variant */
150 return new UUID(randomBytes);
151 }
152
153 /**
154 * Static factory to retrieve a type 3 (name based) {@code UUID} based on
155 * the specified byte array.
156 *
157 * @param name
158 * A byte array to be used to construct a {@code UUID}
159 *
160 * @return A {@code UUID} generated from the specified array
161 */
162 public static UUID nameUUIDFromBytes(byte[] name) {
163 MessageDigest md;
164 try {
165 md = MessageDigest.getInstance("MD5");
166 } catch (NoSuchAlgorithmException nsae) {
167 throw new InternalError("MD5 not supported", nsae);
168 }
169 byte[] md5Bytes = md.digest(name);
170 md5Bytes[6] &= 0x0f; /* clear version */
171 md5Bytes[6] |= 0x30; /* set to version 3 */
172 md5Bytes[8] &= 0x3f; /* clear variant */
173 md5Bytes[8] |= 0x80; /* set to IETF variant */
174 return new UUID(md5Bytes);
175 }
176
177 /**
178 * Creates a {@code UUID} from the string standard representation as
179 * described in the {@link #toString} method.
180 *
181 * @param name
182 * A string that specifies a {@code UUID}
183 *
184 * @return A {@code UUID} with the specified value
185 *
186 * @throws IllegalArgumentException
187 * If name does not conform to the string representation as
188 * described in {@link #toString}
189 *
190 */
191 public static UUID fromString(String name) {
192 String[] components = name.split("-");
193 if (components.length != 5)
194 throw new IllegalArgumentException("Invalid UUID string: "+name);
195 for (int i=0; i<5; i++)
196 components[i] = "0x"+components[i];
197
198 long mostSigBits = Long.decode(components[0]).longValue();
199 mostSigBits <<= 16;
200 mostSigBits |= Long.decode(components[1]).longValue();
201 mostSigBits <<= 16;
202 mostSigBits |= Long.decode(components[2]).longValue();
203
204 long leastSigBits = Long.decode(components[3]).longValue();
205 leastSigBits <<= 48;
206 leastSigBits |= Long.decode(components[4]).longValue();
207
208 return new UUID(mostSigBits, leastSigBits);
209 }
210
211 // Field Accessor Methods
212
213 /**
214 * Returns the least significant 64 bits of this UUID's 128 bit value.
215 *
216 * @return The least significant 64 bits of this UUID's 128 bit value
217 */
218 public long getLeastSignificantBits() {
219 return leastSigBits;
220 }
221
222 /**
223 * Returns the most significant 64 bits of this UUID's 128 bit value.
224 *
225 * @return The most significant 64 bits of this UUID's 128 bit value
226 */
227 public long getMostSignificantBits() {
228 return mostSigBits;
229 }
230
231 /**
232 * The version number associated with this {@code UUID}. The version
233 * number describes how this {@code UUID} was generated.
234 *
235 * The version number has the following meaning:
236 * <p><ul>
237 * <li>1 Time-based UUID
238 * <li>2 DCE security UUID
239 * <li>3 Name-based UUID
240 * <li>4 Randomly generated UUID
241 * </ul>
242 *
243 * @return The version number of this {@code UUID}
244 */
245 public int version() {
246 // Version is bits masked by 0x000000000000F000 in MS long
247 return (int)((mostSigBits >> 12) & 0x0f);
248 }
249
250 /**
251 * The variant number associated with this {@code UUID}. The variant
252 * number describes the layout of the {@code UUID}.
253 *
254 * The variant number has the following meaning:
255 * <p><ul>
256 * <li>0 Reserved for NCS backward compatibility
257 * <li>2 IETF RFC 4122 (Leach-Salz) (used by this class)
258 * <li>6 Reserved, Microsoft Corporation backward compatibility
259 * <li>7 Reserved for future definition
260 * </ul>
261 *
262 * @return The variant number of this {@code UUID}
263 */
264 public int variant() {
265 // This field is composed of a varying number of bits.
266 // 0 - - Reserved for NCS backward compatibility
267 // 1 0 - The Leach-Salz aka IETF variant (used by this class)
268 // 1 1 0 Reserved, Microsoft backward compatibility
269 // 1 1 1 Reserved for future definition.
270 return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
271 & (leastSigBits >> 63));
272 }
273
274 /**
275 * The timestamp value associated with this UUID.
276 *
277 * <p> The 60 bit timestamp value is constructed from the time_low,
278 * time_mid, and time_hi fields of this {@code UUID}. The resulting
279 * timestamp is measured in 100-nanosecond units since midnight,
280 * October 15, 1582 UTC.
281 *
282 * <p> The timestamp value is only meaningful in a time-based UUID, which
283 * has version type 1. If this {@code UUID} is not a time-based UUID then
284 * this method throws UnsupportedOperationException.
285 *
286 * @throws UnsupportedOperationException
287 * If this UUID is not a version 1 UUID
288 */
289 public long timestamp() {
290 if (version() != 1) {
291 throw new UnsupportedOperationException("Not a time-based UUID");
292 }
293
294 return (mostSigBits & 0x0FFFL) << 48
295 | ((mostSigBits >> 16) & 0x0FFFFL) << 32
296 | mostSigBits >>> 32;
297 }
298
299 /**
300 * The clock sequence value associated with this UUID.
301 *
302 * <p> The 14 bit clock sequence value is constructed from the clock
303 * sequence field of this UUID. The clock sequence field is used to
304 * guarantee temporal uniqueness in a time-based UUID.
305 *
306 * <p> The {@code clockSequence} value is only meaningful in a time-based
307 * UUID, which has version type 1. If this UUID is not a time-based UUID
308 * then this method throws UnsupportedOperationException.
309 *
310 * @return The clock sequence of this {@code UUID}
311 *
312 * @throws UnsupportedOperationException
313 * If this UUID is not a version 1 UUID
314 */
315 public int clockSequence() {
316 if (version() != 1) {
317 throw new UnsupportedOperationException("Not a time-based UUID");
318 }
319
320 return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
321 }
322
323 /**
324 * The node value associated with this UUID.
325 *
326 * <p> The 48 bit node value is constructed from the node field of this
327 * UUID. This field is intended to hold the IEEE 802 address of the machine
328 * that generated this UUID to guarantee spatial uniqueness.
329 *
330 * <p> The node value is only meaningful in a time-based UUID, which has
331 * version type 1. If this UUID is not a time-based UUID then this method
332 * throws UnsupportedOperationException.
333 *
334 * @return The node value of this {@code UUID}
335 *
336 * @throws UnsupportedOperationException
337 * If this UUID is not a version 1 UUID
338 */
339 public long node() {
340 if (version() != 1) {
341 throw new UnsupportedOperationException("Not a time-based UUID");
342 }
343
344 return leastSigBits & 0x0000FFFFFFFFFFFFL;
345 }
346
347 // Object Inherited Methods
348
349 /**
350 * Returns a {@code String} object representing this {@code UUID}.
351 *
352 * <p> The UUID string representation is as described by this BNF:
353 * <blockquote><pre>
354 * {@code
355 * UUID = <time_low> "-" <time_mid> "-"
356 * <time_high_and_version> "-"
357 * <variant_and_sequence> "-"
358 * <node>
359 * time_low = 4*<hexOctet>
360 * time_mid = 2*<hexOctet>
361 * time_high_and_version = 2*<hexOctet>
362 * variant_and_sequence = 2*<hexOctet>
363 * node = 6*<hexOctet>
364 * hexOctet = <hexDigit><hexDigit>
365 * hexDigit =
366 * "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
367 * | "a" | "b" | "c" | "d" | "e" | "f"
368 * | "A" | "B" | "C" | "D" | "E" | "F"
369 * }</pre></blockquote>
370 *
371 * @return A string representation of this {@code UUID}
372 */
373 public String toString() {
374 return (digits(mostSigBits >> 32, 8) + "-" +
375 digits(mostSigBits >> 16, 4) + "-" +
376 digits(mostSigBits, 4) + "-" +
377 digits(leastSigBits >> 48, 4) + "-" +
378 digits(leastSigBits, 12));
379 }
380
381 /** Returns val represented by the specified number of hex digits. */
382 private static String digits(long val, int digits) {
383 long hi = 1L << (digits * 4);
384 return Long.toHexString(hi | (val & (hi - 1))).substring(1);
385 }
386
387 /**
388 * Returns a hash code for this {@code UUID}.
389 *
390 * @return A hash code value for this {@code UUID}
391 */
392 public int hashCode() {
393 long hilo = mostSigBits ^ leastSigBits;
394 return ((int)(hilo >> 32)) ^ (int) hilo;
395 }
396
397 /**
398 * Compares this object to the specified object. The result is {@code
399 * true} if and only if the argument is not {@code null}, is a {@code UUID}
400 * object, has the same variant, and contains the same value, bit for bit,
401 * as this {@code UUID}.
402 *
403 * @param obj
404 * The object to be compared
405 *
406 * @return {@code true} if the objects are the same; {@code false}
407 * otherwise
408 */
409 public boolean equals(Object obj) {
410 if ((null == obj) || (obj.getClass() != UUID.class))
411 return false;
412 UUID id = (UUID)obj;
413 return (mostSigBits == id.mostSigBits &&
414 leastSigBits == id.leastSigBits);
415 }
416
417 // Comparison Operations
418
419 /**
420 * Compares this UUID with the specified UUID.
421 *
422 * <p> The first of two UUIDs is greater than the second if the most
423 * significant field in which the UUIDs differ is greater for the first
424 * UUID.
425 *
426 * @param val
427 * {@code UUID} to which this {@code UUID} is to be compared
428 *
429 * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or
430 * greater than {@code val}
431 *
432 */
433 public int compareTo(UUID val) {
434 // The ordering is intentionally set up so that the UUIDs
435 // can simply be numerically compared as two numbers
436 return (this.mostSigBits < val.mostSigBits ? -1 :
437 (this.mostSigBits > val.mostSigBits ? 1 :
438 (this.leastSigBits < val.leastSigBits ? -1 :
439 (this.leastSigBits > val.leastSigBits ? 1 :
440 0))));
441 }
442 }