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="https://en.wikipedia.org/wiki/ISIN">Wikipedia - ISIN</a>
36 * for more details.
37 * </p>
38 *
39 * @since 1.4
40 */
41 public final class ISINCheckDigit extends ModulusCheckDigit {
42
43 private static final long serialVersionUID = -1239211208101323599L;
44
45 private static final int MAX_ALPHANUMERIC_VALUE = 35; // Character.getNumericValue('Z')
46
47 /** Singleton ISIN Check Digit instance */
48 public static final CheckDigit ISIN_CHECK_DIGIT = new ISINCheckDigit();
49
50 /** Weighting given to digits depending on their right position */
51 private static final int[] POSITION_WEIGHT = {2, 1};
52
53 /**
54 * Constructs an ISIN Identifier Check Digit routine.
55 */
56 public ISINCheckDigit() {
57 }
58
59 /**
60 * Calculate the modulus for an ISIN code.
61 *
62 * @param code The code to calculate the modulus for.
63 * @param includesCheckDigit Whether the code includes the Check Digit or not.
64 * @return The modulus value
65 * @throws CheckDigitException if an error occurs calculating the modulus
66 * for the specified code
67 */
68 @Override
69 protected int calculateModulus(final String code, final boolean includesCheckDigit) throws CheckDigitException {
70 final StringBuilder transformed = new StringBuilder(code.length() * 2); // CHECKSTYLE IGNORE MagicNumber
71 if (includesCheckDigit) {
72 final char checkDigit = code.charAt(code.length() - 1); // fetch the last character
73 if (!Character.isDigit(checkDigit)) {
74 throw new CheckDigitException("Invalid checkdigit[" + checkDigit + "] in " + code);
75 }
76 }
77 for (int i = 0; i < code.length(); i++) {
78 final int charValue = Character.getNumericValue(code.charAt(i));
79 if (charValue < 0 || charValue > MAX_ALPHANUMERIC_VALUE) {
80 throw new CheckDigitException("Invalid Character[" + (i + 1) + "] = '" + charValue + "'");
81 }
82 // this converts alphanumerics to two digits
83 // so there is no need to overload toInt()
84 transformed.append(charValue);
85 }
86 return super.calculateModulus(transformed.toString(), includesCheckDigit);
87 }
88
89 /**
90 * <p>Calculates the <i>weighted</i> value of a character in the
91 * code at a specified position.</p>
92 *
93 * <p>For ISIN (from right to left) <b>odd</b> digits are weighted
94 * with a factor of <b>one</b> and <b>even</b> digits with a factor
95 * of <b>two</b>. Weighted values are reduced to their digital root</p>
96 *
97 * @param charValue The numeric value of the character.
98 * @param leftPos The position of the character in the code, counting from left to right
99 * @param rightPos The position of the character in the code, counting from right to left
100 * @return The weighted value of the character.
101 */
102 @Override
103 protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
104 final int weight = POSITION_WEIGHT[rightPos % 2]; // CHECKSTYLE IGNORE MagicNumber
105 final int weightedValue = charValue * weight;
106 return sumDigits(weightedValue);
107 }
108 }