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Java > Open Source Codes > org > apache > turbine > util > GenerateUniqueId


1 package org.apache.turbine.util;
2
3 /*
4  * Copyright 2001-2004 The Apache Software Foundation.
5  *
6  * Licensed under the Apache License, Version 2.0 (the "License")
7  * you may not use this file except in compliance with the License.
8  * You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18
19 import java.util.Random JavaDoc;
20
21 /**
22  * This class generates a unique 10+ character id. This is good for
23  * authenticating users or tracking users around.
24  *
25  * <p>This code was borrowed from Apache
26  * JServ.JServServletManager.java. It is what Apache JServ uses to
27  * generate session ids for users. Unfortunately, it was not included
28  * in Apache JServ as a class, so I had to create one here in order to
29  * use it.
30  *
31  * @author <a HREF="mailto:jon@clearink.com">Jon S. Stevens</a>
32  * @author <a HREF="mailto:neeme@one.lv">Neeme Praks</a>
33  * @version $Id: GenerateUniqueId.java,v 1.3.2.2 2004/05/20 03:16:38 seade Exp $
34  */
35 public class GenerateUniqueId
36 {
37     /*
38      * Create a suitable string for session identification. Use
39      * synchronized count and time to ensure uniqueness. Use random
40      * string to ensure the timestamp cannot be guessed by programmed
41      * attack.
42      *
43      * Format of id is <6 chars random><3 chars time><1+ char count>
44      */
45     static private int session_count = 0;
46     static private long lastTimeVal = 0;
47     static private Random JavaDoc randomSource = new java.util.Random JavaDoc();
48
49     // MAX_RADIX is 36
50
51     /*
52      * We want to have a random string with a length of 6 characters.
53      * Since we encode it BASE 36, we've to modulo it with the
54      * following value:
55      */
56     public final static long maxRandomLen = 2176782336L; // 36 ** 6
57
58     /*
59      * The session identifier must be unique within the typical
60      * lifespan of a Session; the value can roll over after that. 3
61      * characters: (this means a roll over after over a day, which is
62      * much larger than a typical lifespan)
63      */
64     public final static long maxSessionLifespanTics = 46656; // 36 ** 3
65
66     /*
67      * Millisecons between different tics. So this means that the
68      * 3-character time string has a new value every 2 seconds:
69      */
70     public final static long ticDifference = 2000;
71
72     /**
73      * Get the unique id.
74      *
75      * <p>NOTE: This must work together with
76      * get_jserv_session_balance() in jserv_balance.c
77      *
78      * @return A String with the new unique id.
79      */
80     static synchronized public String JavaDoc getIdentifier()
81     {
82         StringBuffer JavaDoc sessionId = new StringBuffer JavaDoc();
83
84         // Random value.
85 long n = randomSource.nextLong();
86         if (n < 0) n = -n;
87         n %= maxRandomLen;
88
89         // Add maxLen to pad the leading characters with '0'; remove
90 // first digit with substring.
91 n += maxRandomLen;
92         sessionId.append(Long.toString(n, Character.MAX_RADIX)
93                 .substring(1));
94
95         long timeVal = (System.currentTimeMillis() / ticDifference);
96
97         // Cut.
98 timeVal %= maxSessionLifespanTics;
99
100         // Padding, see above.
101 timeVal += maxSessionLifespanTics;
102
103         sessionId.append(Long.toString(timeVal, Character.MAX_RADIX)
104                 .substring(1));
105
106         /*
107          * Make the string unique: append the session count since last
108          * time flip.
109          */
110
111         // Count sessions only within tics. So the 'real' session
112 // count isn't exposed to the public.
113 if (lastTimeVal != timeVal)
114         {
115             lastTimeVal = timeVal;
116             session_count = 0;
117         }
118         sessionId.append(Long.toString(++session_count,
119                 Character.MAX_RADIX));
120
121         return sessionId.toString();
122     }
123
124     /**
125      * Get the unique id.
126      *
127      * @param jsIdent A String.
128      * @return A String with the new unique id.
129      */
130     synchronized public String JavaDoc getIdentifier(String JavaDoc jsIdent)
131     {
132         if (jsIdent != null && jsIdent.length() > 0)
133         {
134             return getIdentifier() + "." + jsIdent;
135         }
136         return getIdentifier();
137     }
138
139     /**
140      * Simple test of the functionality.
141      *
142      * @param args A String[] with the command line arguments.
143      */
144     public static void main(String JavaDoc[] args)
145     {
146         System.out.println(GenerateUniqueId.getIdentifier());
147         System.out.println(GenerateUniqueId.getIdentifier());
148         System.out.println(GenerateUniqueId.getIdentifier());
149         System.out.println(GenerateUniqueId.getIdentifier());
150     }
151 }
152
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