001package org.apache.turbine.util;
002
003
004/*
005 * Licensed to the Apache Software Foundation (ASF) under one
006 * or more contributor license agreements.  See the NOTICE file
007 * distributed with this work for additional information
008 * regarding copyright ownership.  The ASF licenses this file
009 * to you under the Apache License, Version 2.0 (the
010 * "License"); you may not use this file except in compliance
011 * with the License.  You may obtain a copy of the License at
012 *
013 *   http://www.apache.org/licenses/LICENSE-2.0
014 *
015 * Unless required by applicable law or agreed to in writing,
016 * software distributed under the License is distributed on an
017 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
018 * KIND, either express or implied.  See the License for the
019 * specific language governing permissions and limitations
020 * under the License.
021 */
022
023
024import java.util.Random;
025
026/**
027 * This class generates a unique 10+ character id.  This is good for
028 * authenticating users or tracking users around.
029 *
030 * <p>This code was borrowed from Apache
031 * JServ.JServServletManager.java.  It is what Apache JServ uses to
032 * generate session ids for users.  Unfortunately, it was not included
033 * in Apache JServ as a class, so I had to create one here in order to
034 * use it.
035 *
036 * @author <a href="mailto:jon@clearink.com">Jon S. Stevens</a>
037 * @author <a href="mailto:neeme@one.lv">Neeme Praks</a>
038 * @version $Id$
039 */
040public class GenerateUniqueId
041{
042    /*
043     * Create a suitable string for session identification.  Use
044     * synchronized count and time to ensure uniqueness.  Use random
045     * string to ensure the timestamp cannot be guessed by programmed
046     * attack.
047     *
048     * Format of id is <6 chars random><3 chars time><1+ char count>
049     */
050    static private int session_count = 0;
051    static private long lastTimeVal = 0;
052    static private Random randomSource = new java.util.Random();
053
054    // MAX_RADIX is 36
055
056    /**
057     * We want to have a random string with a length of 6 characters.
058     * Since we encode it BASE 36, we've to modulo it with the
059     * following value:
060     */
061    public final static long maxRandomLen = 2176782336L; // 36 ** 6
062
063    /**
064     * The session identifier must be unique within the typical
065     * lifespan of a Session; the value can roll over after that.  3
066     * characters: (this means a roll over after over a day, which is
067     * much larger than a typical lifespan)
068     */
069    public final static long maxSessionLifespanTics = 46656; // 36 ** 3
070
071    /**
072     * Millisecons between different tics.  So this means that the
073     * 3-character time string has a new value every 2 seconds:
074     */
075    public final static long ticDifference = 2000;
076
077    /**
078     * Get the unique id.
079     *
080     * <p>NOTE: This must work together with
081     * get_jserv_session_balance() in jserv_balance.c
082     *
083     * @return A String with the new unique id.
084     */
085    static synchronized public String getIdentifier()
086    {
087        StringBuilder sessionId = new StringBuilder();
088
089        // Random value.
090        long n = randomSource.nextLong();
091        if (n < 0)
092        {
093            n = -n;
094        }
095        n %= maxRandomLen;
096
097        // Add maxLen to pad the leading characters with '0'; remove
098        // first digit with substring.
099        n += maxRandomLen;
100        sessionId.append(Long.toString(n, Character.MAX_RADIX)
101                .substring(1));
102
103        long timeVal = (System.currentTimeMillis() / ticDifference);
104
105        // Cut.
106        timeVal %= maxSessionLifespanTics;
107
108        // Padding, see above.
109        timeVal += maxSessionLifespanTics;
110
111        sessionId.append(Long.toString(timeVal, Character.MAX_RADIX)
112                .substring(1));
113
114        /*
115         * Make the string unique: append the session count since last
116         * time flip.
117         */
118
119        // Count sessions only within tics.  So the 'real' session
120        // count isn't exposed to the public.
121        if (lastTimeVal != timeVal)
122        {
123            lastTimeVal = timeVal;
124            session_count = 0;
125        }
126        sessionId.append(Long.toString(++session_count,
127                Character.MAX_RADIX));
128
129        return sessionId.toString();
130    }
131
132    /**
133     * Get the unique id.
134     *
135     * @param jsIdent A String.
136     * @return A String with the new unique id.
137     */
138    synchronized public String getIdentifier(String jsIdent)
139    {
140        if (jsIdent != null && jsIdent.length() > 0)
141        {
142            return getIdentifier() + "." + jsIdent;
143        }
144        return getIdentifier();
145    }
146
147    /**
148     * Simple test of the functionality.
149     *
150     * @param args A String[] with the command line arguments.
151     */
152    public static void main(String[] args)
153    {
154        System.out.println(GenerateUniqueId.getIdentifier());
155        System.out.println(GenerateUniqueId.getIdentifier());
156        System.out.println(GenerateUniqueId.getIdentifier());
157        System.out.println(GenerateUniqueId.getIdentifier());
158    }
159}