| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| package org.apache.bval.extras.constraints.checkdigit; |
| |
| /** |
| * Modulus 10 <b>Luhn</b> Check Digit calculation/validation. |
| * <p> |
| * Luhn check digits are used, for example, by: |
| * <ul> |
| * <li><a href="http://en.wikipedia.org/wiki/Credit_card">Credit Card Numbers</a></li> |
| * <li><a href="http://en.wikipedia.org/wiki/IMEI">IMEI Numbers</a> - International |
| * Mobile Equipment Identity Numbers</li> |
| * </ul> |
| * Check digit calculation is based on <i>modulus 10</i> with digits in |
| * an <i>odd</i> position (from right to left) being weighted 1 and <i>even</i> |
| * position digits being weighted 2 (weighted values greater than 9 have 9 subtracted). |
| * <p> |
| * See <a href="http://en.wikipedia.org/wiki/Luhn_algorithm">Wikipedia</a> |
| * for more details. |
| */ |
| public final class LuhnValidator |
| extends ModulusValidator<Luhn> { |
| |
| /** weighting given to digits depending on their right position */ |
| private static final int[] POSITION_WEIGHT = new int[] {2, 1}; |
| |
| public LuhnValidator() { |
| super(10); |
| } |
| |
| /** |
| * <p>Calculates the <i>weighted</i> value of a charcter in the |
| * code at a specified position.</p> |
| * |
| * <p>For Luhn (from right to left) <b>odd</b> digits are weighted |
| * with a factor of <b>one</b> and <b>even</b> digits with a factor |
| * of <b>two</b>. Weighted values > 9, have 9 subtracted</p> |
| * |
| * {@inheritDoc} |
| */ |
| @Override |
| protected int weightedValue( int charValue, int leftPos, int rightPos ) |
| throws Exception { |
| int weight = POSITION_WEIGHT[rightPos % 2]; |
| int weightedValue = (charValue * weight); |
| return (weightedValue > 9 ? (weightedValue - 9) : weightedValue); |
| } |
| |
| } |