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    1   package org.apache.turbine.util;
    2
    3
    4   /*
    5    * Licensed to the Apache Software Foundation (ASF) under one
    6    * or more contributor license agreements.  See the NOTICE file
    7    * distributed with this work for additional information
    8    * regarding copyright ownership.  The ASF licenses this file
    9    * to you under the Apache License, Version 2.0 (the
    10   * "License"); you may not use this file except in compliance
    11   * with the License.  You may obtain a copy of the License at
    12   *
    13   *   http://www.apache.org/licenses/LICENSE-2.0
    14   *
    15   * Unless required by applicable law or agreed to in writing,
    16   * software distributed under the License is distributed on an
    17   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    18   * KIND, either express or implied.  See the License for the
    19   * specific language governing permissions and limitations
    20   * under the License.
    21   */
    22
    23
    24  import java.util.Random;
    25
    26  /**
    27   * This class generates a unique 10+ character id.  This is good for
    28   * authenticating users or tracking users around.
    29   *
    30   * <p>This code was borrowed from Apache
    31   * JServ.JServServletManager.java.  It is what Apache JServ uses to
    32   * generate session ids for users.  Unfortunately, it was not included
    33   * in Apache JServ as a class, so I had to create one here in order to
    34   * use it.
    35   *
    36   * @author <a href="mailto:jon@clearink.com">Jon S. Stevens</a>
    37   * @author <a href="mailto:neeme@one.lv">Neeme Praks</a>
    38   * @version $Id: GenerateUniqueId.java 1709648 2015-10-20 17:08:10Z tv $
    39   */
    40  public class GenerateUniqueId
    41  {
    42      /*
    43       * Create a suitable string for session identification.  Use
    44       * synchronized count and time to ensure uniqueness.  Use random
    45       * string to ensure the timestamp cannot be guessed by programmed
    46       * attack.
    47       *
    48       * Format of id is <6 chars random><3 chars time><1+ char count>
    49       */
    50      static private int session_count = 0;
    51      static private long lastTimeVal = 0;
    52      static private Random randomSource = new java.util.Random();
    53
    54      // MAX_RADIX is 36
    55
    56      /**
    57       * We want to have a random string with a length of 6 characters.
    58       * Since we encode it BASE 36, we've to modulo it with the
    59       * following value:
    60       */
    61      public final static long maxRandomLen = 2176782336L; // 36 ** 6
    62
    63      /**
    64       * The session identifier must be unique within the typical
    65       * lifespan of a Session; the value can roll over after that.  3
    66       * characters: (this means a roll over after over a day, which is
    67       * much larger than a typical lifespan)
    68       */
    69      public final static long maxSessionLifespanTics = 46656; // 36 ** 3
    70
    71      /**
    72       * Millisecons between different tics.  So this means that the
    73       * 3-character time string has a new value every 2 seconds:
    74       */
    75      public final static long ticDifference = 2000;
    76
    77      /**
    78       * Get the unique id.
    79       *
    80       * <p>NOTE: This must work together with
    81       * get_jserv_session_balance() in jserv_balance.c
    82       *
    83       * @return A String with the new unique id.
    84       */
    85      static synchronized public String getIdentifier()
    86      {
    87          StringBuilder sessionId = new StringBuilder();
    88
    89          // Random value.
    90          long n = randomSource.nextLong();
    91          if (n < 0)
    92          {
    93              n = -n;
    94          }
    95          n %= maxRandomLen;
    96
    97          // Add maxLen to pad the leading characters with '0'; remove
    98          // first digit with substring.
    99          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 }