View Javadoc
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.routines.checkdigit;
18  
19  /**
20   * Modulus 10 <b>ISIN</b> (International Securities Identifying Number) Check Digit calculation/validation.
21   *
22   * <p>
23   * ISIN Numbers are 12 character alphanumeric codes used
24   * to identify Securities.
25   * </p>
26   *
27   * <p>
28   * Check digit calculation uses the <i>Modulus 10 Double Add Double</i> technique
29   * with every second digit being weighted by 2. Alphabetic characters are
30   * converted to numbers by their position in the alphabet starting with A being 10.
31   * Weighted numbers greater than ten are treated as two separate numbers.
32   * </p>
33   *
34   * <p>
35   * See <a href="http://en.wikipedia.org/wiki/ISIN">Wikipedia - ISIN</a>
36   * for more details.
37   * </p>
38   *
39   * @version $Revision: 1739356 $
40   * @since Validator 1.4
41   */
42  public final class ISINCheckDigit extends ModulusCheckDigit {
43  
44      private static final long serialVersionUID = -1239211208101323599L;
45  
46      private static final int MAX_ALPHANUMERIC_VALUE = 35; // Character.getNumericValue('Z')
47  
48      /** Singleton ISIN Check Digit instance */
49      public static final CheckDigit ISIN_CHECK_DIGIT = new ISINCheckDigit();
50  
51      /** weighting given to digits depending on their right position */
52      private static final int[] POSITION_WEIGHT = new int[] {2, 1};
53  
54      /**
55       * Construct an ISIN Indetifier Check Digit routine.
56       */
57      public ISINCheckDigit() {
58          super(10); // CHECKSTYLE IGNORE MagicNumber
59      }
60  
61      /**
62       * Calculate the modulus for an ISIN code.
63       *
64       * @param code The code to calculate the modulus for.
65       * @param includesCheckDigit Whether the code includes the Check Digit or not.
66       * @return The modulus value
67       * @throws CheckDigitException if an error occurs calculating the modulus
68       * for the specified code
69       */
70      @Override
71      protected int calculateModulus(String code, boolean includesCheckDigit) throws CheckDigitException {
72          StringBuilder transformed = new  StringBuilder(code.length() * 2);
73          if (includesCheckDigit) {
74              char checkDigit = code.charAt(code.length()-1); // fetch the last character
75              if (!Character.isDigit(checkDigit)){
76                  throw new CheckDigitException("Invalid checkdigit["+ checkDigit+ "] in " + code);
77              }
78          }
79          for (int i = 0; i < code.length(); i++) {
80              int charValue = Character.getNumericValue(code.charAt(i));
81              if (charValue < 0 || charValue > MAX_ALPHANUMERIC_VALUE) {
82                  throw new CheckDigitException("Invalid Character[" +
83                          (i + 1) + "] = '" + charValue + "'");
84              }
85               // this converts alphanumerics to two digits
86               // so there is no need to overload toInt()
87              transformed.append(charValue);
88          }
89          return super.calculateModulus(transformed.toString(), includesCheckDigit);
90      }
91  
92      /**
93       * <p>Calculates the <i>weighted</i> value of a charcter in the
94       * code at a specified position.</p>
95       *
96       * <p>For Luhn (from right to left) <b>odd</b> digits are weighted
97       * with a factor of <b>one</b> and <b>even</b> digits with a factor
98       * of <b>two</b>. Weighted values &gt; 9, have 9 subtracted</p>
99       *
100      * @param charValue The numeric value of the character.
101      * @param leftPos The position of the character in the code, counting from left to right
102      * @param rightPos The positionof the character in the code, counting from right to left
103      * @return The weighted value of the character.
104      */
105     @Override
106     protected int weightedValue(int charValue, int leftPos, int rightPos) {
107         int weight = POSITION_WEIGHT[rightPos % 2];
108         int weightedValue = (charValue * weight);
109         return ModulusCheckDigit.sumDigits(weightedValue);
110     }
111 }