UUID


1   /*
2    * @(#)UUID.java    1.14 04/07/12
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.util;
9   
10  import java.security.*;
11  import java.io.IOException  ;
12  import java.io.UnsupportedEncodingException  ;
13  
14  /**
15   * 
16   * A class that represents an immutable universally unique identifier (UUID). 
17   * A UUID represents a 128-bit value.
18   *
19   * <p>There exist different variants of these global identifiers. The methods
20   * of this class are for manipulating the Leach-Salz variant, although the
21   * constructors allow the creation of any variant of UUID (described below).
22   * 
23   * <p>The layout of a variant 2 (Leach-Salz) UUID is as follows:
24   *
25   * The most significant long consists of the following unsigned fields:
26   * <pre>
27   * 0xFFFFFFFF00000000 time_low
28   * 0x00000000FFFF0000 time_mid
29   * 0x000000000000F000 version
30   * 0x0000000000000FFF time_hi
31   * </pre>
32   * The least significant long consists of the following unsigned fields:
33   * <pre>
34   * 0xC000000000000000 variant
35   * 0x3FFF000000000000 clock_seq
36   * 0x0000FFFFFFFFFFFF node
37   * </pre>
38   *
39   * <p>The variant field contains a value which identifies the layout of
40   * the <tt>UUID</tt>. The bit layout described above is valid only for
41   * a <tt>UUID</tt> with a variant value of 2, which indicates the
42   * Leach-Salz variant.
43   *
44   * <p>The version field holds a value that describes the type of this
45   * <tt>UUID</tt>. There are four different basic types of UUIDs: time-based,
46   * DCE security, name-based, and randomly generated UUIDs. These types
47   * have a version value of 1, 2, 3 and 4, respectively.
48   * 
49   * <p>For more information including algorithms used to create <tt>UUID</tt>s,
50   * see the Internet-Draft <a HREF="http://www.ietf.org/internet-drafts/draft-mealling-uuid-urn-03.txt">UUIDs and GUIDs</a>
51   * or the standards body definition at
52   * <a HREF="http://www.iso.ch/cate/d2229.html">ISO/IEC 11578:1996</a>.
53   *
54   * @version 1.14, 07/12/04
55   * @since   1.5
56   */
57  public final class UUID 
58  implements java.io.Serializable  , Comparable  <UUID  > {
59  
60      /**
61       * Explicit serialVersionUID for interoperability.
62       */
63       private static final long serialVersionUID = -4856846361193249489L;
64  
65      /*
66       * The most significant 64 bits of this UUID.
67       *
68       * @serial
69       */
70      private final long mostSigBits;
71  
72      /*
73       * The least significant 64 bits of this UUID.
74       *
75       * @serial
76       */
77      private final long leastSigBits;
78  
79      /*
80       * The version number associated with this UUID. Computed on demand.
81       */
82      private transient int version = -1;
83  
84      /*
85       * The variant number associated with this UUID. Computed on demand.
86       */
87      private transient int variant = -1;
88  
89      /*
90       * The timestamp associated with this UUID. Computed on demand.
91       */
92      private transient volatile long timestamp = -1;
93  
94      /*
95       * The clock sequence associated with this UUID. Computed on demand.
96       */
97      private transient int sequence = -1;
98  
99      /*
100      * The node number associated with this UUID. Computed on demand.
101      */
102     private transient long node = -1;
103 
104     /*
105      * The hashcode of this UUID. Computed on demand.
106      */
107     private transient int hashCode = -1;
108 
109     /*
110      * The random number generator used by this class to create random
111      * based UUIDs.
112      */
113     private static volatile SecureRandom numberGenerator = null;
114 
115     // Constructors and Factories
116 
117     /*
118      * Private constructor which uses a byte array to construct the new UUID.
119      */
120     private UUID(byte[] data) {
121         long msb = 0;
122         long lsb = 0;
123         assert data.length == 16;
124         for (int i=0; i<8; i++)
125             msb = (msb << 8) | (data[i] & 0xff);
126         for (int i=8; i<16; i++)
127             lsb = (lsb << 8) | (data[i] & 0xff);
128         this.mostSigBits = msb;
129         this.leastSigBits = lsb;
130     }
131 
132     /**
133      * Constructs a new <tt>UUID</tt> using the specified data.
134      * <tt>mostSigBits</tt> is used for the most significant 64 bits
135      * of the <tt>UUID</tt> and <tt>leastSigBits</tt> becomes the
136      * least significant 64 bits of the <tt>UUID</tt>.
137      *
138      * @param  mostSigBits
139      * @param  leastSigBits
140      */
141     public UUID(long mostSigBits, long leastSigBits) {
142         this.mostSigBits = mostSigBits;
143         this.leastSigBits = leastSigBits;
144     }
145 
146     /**
147      * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
148      *
149      * The <code>UUID</code> is generated using a cryptographically strong
150      * pseudo random number generator.
151      *
152      * @return  a randomly generated <tt>UUID</tt>.
153      */
154     public static UUID   randomUUID() {
155         SecureRandom ng = numberGenerator;
156         if (ng == null) {
157             numberGenerator = ng = new SecureRandom();
158         }
159 
160         byte[] randomBytes = new byte[16];
161         ng.nextBytes(randomBytes);
162         randomBytes[6]  &= 0x0f;  /* clear version        */
163         randomBytes[6]  |= 0x40;  /* set to version 4     */
164         randomBytes[8]  &= 0x3f;  /* clear variant        */
165         randomBytes[8]  |= 0x80;  /* set to IETF variant  */
166         UUID   result = new UUID  (randomBytes);
167         return new UUID  (randomBytes);
168     }
169 
170     /**
171      * Static factory to retrieve a type 3 (name based) <tt>UUID</tt> based on
172      * the specified byte array.
173      *
174      * @param  name a byte array to be used to construct a <tt>UUID</tt>.
175      * @return  a <tt>UUID</tt> generated from the specified array.
176      */
177     public static UUID   nameUUIDFromBytes(byte[] name) {
178         MessageDigest md;
179         try {
180             md = MessageDigest.getInstance("MD5");
181         } catch (NoSuchAlgorithmException nsae) {
182             throw new InternalError  ("MD5 not supported");
183         }
184         byte[] md5Bytes = md.digest(name);
185         md5Bytes[6]  &= 0x0f;  /* clear version        */
186         md5Bytes[6]  |= 0x30;  /* set to version 3     */
187         md5Bytes[8]  &= 0x3f;  /* clear variant        */
188         md5Bytes[8]  |= 0x80;  /* set to IETF variant  */
189         return new UUID  (md5Bytes);
190     }
191 
192     /**
193      * Creates a <tt>UUID</tt> from the string standard representation as
194      * described in the {@link #toString} method.
195      *
196      * @param  name a string that specifies a <tt>UUID</tt>.
197      * @return  a <tt>UUID</tt> with the specified value.
198      * @throws IllegalArgumentException if name does not conform to the
199      *         string representation as described in {@link #toString}.
200      */
201     public static UUID   fromString(String   name) {
202         String  [] components = name.split("-");
203         if (components.length != 5)
204             throw new IllegalArgumentException  ("Invalid UUID string: "+name);
205         for (int i=0; i<5; i++)
206             components[i] = "0x"+components[i];
207 
208         long mostSigBits = Long.decode(components[0]).longValue();
209         mostSigBits <<= 16;
210         mostSigBits |= Long.decode(components[1]).longValue();
211         mostSigBits <<= 16;
212         mostSigBits |= Long.decode(components[2]).longValue();
213 
214         long leastSigBits = Long.decode(components[3]).longValue();
215         leastSigBits <<= 48;
216         leastSigBits |= Long.decode(components[4]).longValue();
217 
218         return new UUID  (mostSigBits, leastSigBits);
219     }
220 
221     // Field Accessor Methods
222 
223     /**
224      * Returns the least significant 64 bits of this UUID's 128 bit value.
225      *
226      * @return the least significant 64 bits of this UUID's 128 bit value.
227      */
228     public long getLeastSignificantBits() {
229         return leastSigBits;
230     }
231 
232     /**
233      * Returns the most significant 64 bits of this UUID's 128 bit value.
234      *
235      * @return the most significant 64 bits of this UUID's 128 bit value.
236      */
237     public long getMostSignificantBits() {
238         return mostSigBits;
239     }
240 
241     /**
242      * The version number associated with this <tt>UUID</tt>. The version 
243      * number describes how this <tt>UUID</tt> was generated.
244      *
245      * The version number has the following meaning:<p>
246      * <ul>
247      * <li>1    Time-based UUID
248      * <li>2    DCE security UUID
249      * <li>3    Name-based UUID
250      * <li>4    Randomly generated UUID
251      * </ul>
252      *
253      * @return  the version number of this <tt>UUID</tt>.
254      */
255     public int version() {
256         if (version < 0) {
257             // Version is bits masked by 0x000000000000F000 in MS long
258             version = (int)((mostSigBits >> 12) & 0x0f);
259         }
260         return version;
261     }
262 
263     /**
264      * The variant number associated with this <tt>UUID</tt>. The variant 
265      * number describes the layout of the <tt>UUID</tt>.
266      *
267      * The variant number has the following meaning:<p>
268      * <ul>
269      * <li>0    Reserved for NCS backward compatibility
270      * <li>2    The Leach-Salz variant (used by this class)
271      * <li>6    Reserved, Microsoft Corporation backward compatibility
272      * <li>7    Reserved for future definition
273      * </ul>
274      *
275      * @return  the variant number of this <tt>UUID</tt>.
276      */
277     public int variant() {
278         if (variant < 0) {
279             // This field is composed of a varying number of bits
280             if ((leastSigBits >>> 63) == 0) {
281                 variant = 0;
282             } else if ((leastSigBits >>> 62) == 2) {
283                 variant = 2;
284             } else {
285                 variant = (int)(leastSigBits >>> 61);
286             }
287         }
288         return variant;
289     }
290 
291     /**
292      * The timestamp value associated with this UUID.
293      *
294      * <p>The 60 bit timestamp value is constructed from the time_low,
295      * time_mid, and time_hi fields of this <tt>UUID</tt>. The resulting 
296      * timestamp is measured in 100-nanosecond units since midnight, 
297      * October 15, 1582 UTC.<p>
298      *
299      * The timestamp value is only meaningful in a time-based UUID, which
300      * has version type 1. If this <tt>UUID</tt> is not a time-based UUID then
301      * this method throws UnsupportedOperationException.
302      * 
303      * @throws UnsupportedOperationException if this UUID is not a 
304      *         version 1 UUID.
305      */
306     public long timestamp() {
307         if (version() != 1) {
308             throw new UnsupportedOperationException  ("Not a time-based UUID");
309         }
310         long result = timestamp;
311         if (result < 0) {
312             result = (mostSigBits & 0x0000000000000FFFL) << 48;
313             result |= ((mostSigBits >> 16) & 0xFFFFL) << 32;
314             result |= mostSigBits >>> 32;
315             timestamp = result;
316         }
317         return result;
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.<p>
326      *
327      * The  clockSequence value is only meaningful in a time-based UUID, which
328      * has version type 1. If this UUID is not a time-based UUID then
329      * this method throws UnsupportedOperationException.
330      * 
331      * @return  the clock sequence of this <tt>UUID</tt>.
332      * @throws UnsupportedOperationException if this UUID is not a 
333      *         version 1 UUID.
334      */
335     public int clockSequence() {
336         if (version() != 1) {
337             throw new UnsupportedOperationException  ("Not a time-based UUID");
338         }
339         if (sequence < 0) {
340             sequence = (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
341         }
342         return sequence;
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
349      * this UUID. This field is intended to hold the IEEE 802 address 
350      * of the machine that generated this UUID to guarantee spatial
351      * uniqueness.<p>
352      *
353      * The node value is only meaningful in a time-based UUID, which
354      * has version type 1. If this UUID is not a time-based UUID then
355      * this method throws UnsupportedOperationException.
356      * 
357      * @return  the node value of this <tt>UUID</tt>.
358      * @throws UnsupportedOperationException if this UUID is not a
359      *         version 1 UUID.
360      */
361     public long node() {
362         if (version() != 1) {
363             throw new UnsupportedOperationException  ("Not a time-based UUID");
364         }
365         if (node < 0) {
366             node = leastSigBits & 0x0000FFFFFFFFFFFFL;
367         }
368         return node;
369     }
370 
371     // Object Inherited Methods
372 
373     /**
374      * Returns a <code>String</code> object representing this
375      * <code>UUID</code>.
376      * 
377      * <p>The UUID string representation is as described by this BNF : 
378      * <pre>
379      *  UUID                   = <time_low> "-" <time_mid> "-"
380      *                           <time_high_and_version> "-"
381      *                           <variant_and_sequence> "-"
382      *                           <node>
383      *  time_low               = 4*<hexOctet>
384      *  time_mid               = 2*<hexOctet>
385      *  time_high_and_version  = 2*<hexOctet>
386      *  variant_and_sequence   = 2*<hexOctet>
387      *  node                   = 6*<hexOctet>
388      *  hexOctet               = <hexDigit><hexDigit>
389      *  hexDigit               =
390      *        "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
391      *        | "a" | "b" | "c" | "d" | "e" | "f"
392      *        | "A" | "B" | "C" | "D" | "E" | "F"
393      * </pre>
394      *
395      * @return  a string representation of this <tt>UUID</tt>.
396      */
397     public String   toString() {
398     return (digits(mostSigBits >> 32, 8) + "-" +
399         digits(mostSigBits >> 16, 4) + "-" +
400         digits(mostSigBits, 4) + "-" +
401         digits(leastSigBits >> 48, 4) + "-" +
402         digits(leastSigBits, 12));
403     }
404 
405     /** Returns val represented by the specified number of hex digits. */
406     private static String   digits(long val, int digits) {
407     long hi = 1L << (digits * 4);
408     return Long.toHexString(hi | (val & (hi - 1))).substring(1);
409     }
410 
411     /**
412      * Returns a hash code for this <code>UUID</code>.
413      *
414      * @return  a hash code value for this <tt>UUID</tt>. 
415      */
416     public int hashCode() {
417         if (hashCode == -1) {
418             hashCode = (int)((mostSigBits >> 32) ^
419                              mostSigBits ^
420                              (leastSigBits >> 32) ^
421                              leastSigBits);
422         }
423         return hashCode;
424     }
425 
426     /**
427      * Compares this object to the specified object.  The result is
428      * <tt>true</tt> if and only if the argument is not
429      * <tt>null</tt>, is a <tt>UUID</tt> object, has the same variant,
430      * and contains the same value, bit for bit, as this <tt>UUID</tt>.
431      *
432      * @param   obj   the object to compare with.
433      * @return  <code>true</code> if the objects are the same;
434      *          <code>false</code> otherwise.
435      */
436     public boolean equals(Object   obj) {
437     if (!(obj instanceof UUID  ))
438         return false;
439         if (((UUID  )obj).variant() != this.variant())
440             return false;
441         UUID   id = (UUID  )obj;
442     return (mostSigBits == id.mostSigBits &&
443                 leastSigBits == id.leastSigBits);
444     }
445 
446     // Comparison Operations
447 
448     /**
449      * Compares this UUID with the specified UUID.
450      * 
451      * <p>The first of two UUIDs follows the second if the most significant
452      * field in which the UUIDs differ is greater for the first UUID.
453      *
454      * @param  val <tt>UUID</tt> to which this <tt>UUID</tt> is to be compared.
455      * @return -1, 0 or 1 as this <tt>UUID</tt> is less than, equal
456      *         to, or greater than <tt>val</tt>.
457      */
458     public int compareTo(UUID   val) {
459         // The ordering is intentionally set up so that the UUIDs
460         // can simply be numerically compared as two numbers
461         return (this.mostSigBits < val.mostSigBits ? -1 : 
462                 (this.mostSigBits > val.mostSigBits ? 1 :
463                  (this.leastSigBits < val.leastSigBits ? -1 :
464                   (this.leastSigBits > val.leastSigBits ? 1 :
465                    0))));
466     }
467 
468     /**
469      * Reconstitute the <tt>UUID</tt> instance from a stream (that is,
470      * deserialize it). This is necessary to set the transient fields
471      * to their correct uninitialized value so they will be recomputed
472      * on demand.
473      */
474     private void readObject(java.io.ObjectInputStream   in)
475         throws java.io.IOException  , ClassNotFoundException   {
476 
477         in.defaultReadObject();
478 
479         // Set "cached computation" fields to their initial values
480         version = -1;
481         variant = -1;
482         timestamp = -1;
483         sequence = -1;
484         node = -1;
485         hashCode = -1;
486     }
487 }
488
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