001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.validator.routines.checkdigit;
018
019 import java.io.Serializable;
020
021 /**
022 * <b>Verhoeff</b> (Dihedral) Check Digit calculation/validation.
023 * <p>
024 * Check digit calculation for numeric codes using a
025 * <a href="http://en.wikipedia.org/wiki/Dihedral_group">Dihedral Group</a>
026 * of order 10.
027 * <p>
028 * See <a href="http://en.wikipedia.org/wiki/Verhoeff_algorithm">Wikipedia
029 * - Verhoeff algorithm</a> for more details.
030 *
031 * @version $Revision: 493905 $ $Date: 2007-01-08 03:11:38 +0100 (Mo, 08. Jan 2007) $
032 * @since Validator 1.4
033 */
034 public final class VerhoeffCheckDigit implements CheckDigit, Serializable {
035
036 /** Singleton Verhoeff Check Digit instance */
037 public static final CheckDigit INSTANCE = new VerhoeffCheckDigit();
038
039 /** D - multiplication table */
040 private static final int[][] D_TABLE = new int[][] {
041 {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
042 {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
043 {2, 3, 4, 0, 1, 7, 8, 9, 5, 6},
044 {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
045 {4, 0, 1, 2, 3, 9, 5, 6, 7, 8},
046 {5, 9, 8, 7, 6, 0, 4, 3, 2, 1},
047 {6, 5, 9, 8, 7, 1, 0, 4, 3, 2},
048 {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
049 {8, 7, 6, 5, 9, 3, 2, 1, 0, 4},
050 {9, 8, 7, 6, 5, 4, 3, 2, 1, 0}};
051
052 /** P - permutation table */
053 private static final int[][] P_TABLE = new int[][] {
054 {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
055 {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
056 {5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
057 {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
058 {9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
059 {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
060 {2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
061 {7, 0, 4, 6, 9, 1, 3, 2, 5, 8}};
062
063 /** inv: inverse table */
064 private static final int[] INV_TABLE = new int[]
065 {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};
066
067
068 /**
069 * Validate the Verhoeff <i>Check Digit</i> for a code.
070 *
071 * @param code The code to validate
072 * @return <code>true</code> if the check digit is valid,
073 * otherwise <code>false</code>
074 */
075 public boolean isValid(String code) {
076 if (code == null || code.length() == 0) {
077 return false;
078 }
079 try {
080 return (calculateChecksum(code, true) == 0);
081 } catch (CheckDigitException e) {
082 return false;
083 }
084 }
085
086 /**
087 * Calculate a Verhoeff <i>Check Digit</i> for a code.
088 *
089 * @param code The code to calculate the Check Digit for
090 * @return The calculated Check Digit
091 * @throws CheckDigitException if an error occurs calculating
092 * the check digit for the specified code
093 */
094 public String calculate(String code) throws CheckDigitException {
095 if (code == null || code.length() == 0) {
096 throw new CheckDigitException("Code is missing");
097 }
098 int checksum = calculateChecksum(code, false);
099 return Integer.toString(INV_TABLE[checksum]);
100 }
101
102 /**
103 * Calculate the checksum.
104 *
105 * @param code The code to calculate the checksum for.
106 * @param includesCheckDigit Whether the code includes the Check Digit or not.
107 * @return The checksum value
108 * @throws CheckDigitException if the code contains an invalid character (i.e. not numeric)
109 */
110 private int calculateChecksum(String code, boolean includesCheckDigit) throws CheckDigitException {
111 int checksum = 0;
112 for (int i = 0; i < code.length(); i++) {
113 int idx = code.length() - (i + 1);
114 int num = Character.getNumericValue(code.charAt(idx));
115 if (num < 0 || num > 9) {
116 throw new CheckDigitException("Invalid Character[" +
117 i + "] = '" + ((int)code.charAt(idx)) + "'");
118 }
119 int pos = includesCheckDigit ? i : i + 1;
120 checksum = D_TABLE[checksum][P_TABLE[pos % 8][num]];
121 }
122 return checksum;
123 }
124
125 }