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    1   /*
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements.  See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License.  You may obtain a copy of the License at
    8    *
    9    *      http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17  package org.apache.commons.validator;
    18
    19  import org.apache.oro.text.perl.Perl5Util;
    20
    21  /***
    22   * A class for validating 10 digit ISBN codes.
    23   * Based on this
    24   * <a href="http://www.isbn.org/standards/home/isbn/international/html/usm4.htm">
    25   * algorithm</a>
    26   *
    27   * @version $Revision: 478334 $ $Date: 2006-11-22 21:31:54 +0000 (Wed, 22 Nov 2006) $
    28   * @since Validator 1.2.0
    29   */
    30  public class ISBNValidator {
    31
    32      private static final String SEP = "(//-|//s)";
    33      private static final String GROUP = "(//d{1,5})";
    34      private static final String PUBLISHER = "(//d{1,7})";
    35      private static final String TITLE = "(//d{1,6})";
    36      private static final String CHECK = "([0-9X])";
    37
    38      /***
    39       * ISBN consists of 4 groups of numbers separated by either dashes (-)
    40       * or spaces.  The first group is 1-5 characters, second 1-7, third 1-6,
    41       * and fourth is 1 digit or an X.
    42       */
    43      private static final String ISBN_PATTERN =
    44          "/^" + GROUP + SEP + PUBLISHER + SEP + TITLE + SEP + CHECK + "$/";
    45
    46      /***
    47       * Default Constructor.
    48       */
    49      public ISBNValidator() {
    50          super();
    51      }
    52
    53      /***
    54       * If the ISBN is formatted with space or dash separators its format is
    55       * validated.  Then the digits in the number are weighted, summed, and
    56       * divided by 11 according to the ISBN algorithm.  If the result is zero,
    57       * the ISBN is valid.  This method accepts formatted or raw ISBN codes.
    58       *
    59       * @param isbn Candidate ISBN number to be validated. <code>null</code> is
    60       * considered invalid.
    61       * @return true if the string is a valid ISBN code.
    62       */
    63      public boolean isValid(String isbn) {
    64          if (isbn == null || isbn.length() < 10 || isbn.length() > 13) {
    65              return false;
    66          }
    67
    68          if (isFormatted(isbn) && !isValidPattern(isbn)) {
    69              return false;
    70          }
    71
    72          isbn = clean(isbn);
    73          if (isbn.length() != 10) {
    74              return false;
    75          }
    76
    77          return (sum(isbn) % 11) == 0;
    78      }
    79
    80      /***
    81       * Returns the sum of the weighted ISBN characters.
    82       */
    83      private int sum(String isbn) {
    84          int total = 0;
    85          for (int i = 0; i < 9; i++) {
    86              int weight = 10 - i;
    87              total += (weight * toInt(isbn.charAt(i)));
    88          }
    89          total += toInt(isbn.charAt(9)); // add check digit
    90          return total;
    91      }
    92
    93      /***
    94       * Removes all non-digit characters except for 'X' which is a valid ISBN
    95       * character.
    96       */
    97      private String clean(String isbn) {
    98          StringBuffer buf = new StringBuffer(10);
    99
    100         for (int i = 0; i < isbn.length(); i++) {
    101             char digit = isbn.charAt(i);
    102             if (Character.isDigit(digit) || (digit == 'X')) {
    103                 buf.append(digit);
    104             }
    105         }
    106
    107         return buf.toString();
    108     }
    109
    110     /***
    111      * Returns the numeric value represented by the character.  If the
    112      * character is not a digit but an 'X', 10 is returned.
    113      */
    114     private int toInt(char ch) {
    115         return (ch == 'X') ? 10 : Character.getNumericValue(ch);
    116     }
    117
    118     /***
    119      * Returns true if the ISBN contains one of the separator characters space
    120      * or dash.
    121      */
    122     private boolean isFormatted(String isbn) {
    123         return ((isbn.indexOf('-') != -1) || (isbn.indexOf(' ') != -1));
    124     }
    125
    126     /***
    127      * Returns true if the ISBN is formatted properly.
    128      */
    129     private boolean isValidPattern(String isbn) {
    130         return new Perl5Util().match(ISBN_PATTERN, isbn);
    131     }
    132
    133 }