org.apache.commons.validator.routines.checkdigit.VerhoeffCheckDigit.java Source code

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Here is the source code for org.apache.commons.validator.routines.checkdigit.VerhoeffCheckDigit.java

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/*
 * 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.commons.validator.routines.checkdigit;

import java.io.Serializable;

/**
 * <b>Verhoeff</b> (Dihedral) Check Digit calculation/validation.
 * <p>
 * Check digit calculation for numeric codes using a <a href="http://en.wikipedia.org/wiki/Dihedral_group">Dihedral Group</a> of
 * order 10.
 * <p>
 * See <a href="http://en.wikipedia.org/wiki/Verhoeff_algorithm">Wikipedia - Verhoeff algorithm</a> for more details.
 * 
 * @version $Revision: 909009 $ $Date: 2010-02-11 14:59:45 +0000 (Qui, 11 Fev 2010) $
 * @since Validator 1.4
 */
public final class VerhoeffCheckDigit implements CheckDigit, Serializable {

    /** Singleton Verhoeff Check Digit instance */
    public static final CheckDigit VERHOEFF_CHECK_DIGIT = new VerhoeffCheckDigit();

    /** D - multiplication table */
    private static final int[][] D_TABLE = new int[][] { { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
            { 1, 2, 3, 4, 0, 6, 7, 8, 9, 5 }, { 2, 3, 4, 0, 1, 7, 8, 9, 5, 6 }, { 3, 4, 0, 1, 2, 8, 9, 5, 6, 7 },
            { 4, 0, 1, 2, 3, 9, 5, 6, 7, 8 }, { 5, 9, 8, 7, 6, 0, 4, 3, 2, 1 }, { 6, 5, 9, 8, 7, 1, 0, 4, 3, 2 },
            { 7, 6, 5, 9, 8, 2, 1, 0, 4, 3 }, { 8, 7, 6, 5, 9, 3, 2, 1, 0, 4 }, { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 } };

    /** P - permutation table */
    private static final int[][] P_TABLE = new int[][] { { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
            { 1, 5, 7, 6, 2, 8, 3, 0, 9, 4 }, { 5, 8, 0, 3, 7, 9, 6, 1, 4, 2 }, { 8, 9, 1, 6, 0, 4, 3, 5, 2, 7 },
            { 9, 4, 5, 3, 1, 2, 6, 8, 7, 0 }, { 4, 2, 8, 6, 5, 7, 3, 9, 0, 1 }, { 2, 7, 9, 3, 8, 0, 6, 4, 1, 5 },
            { 7, 0, 4, 6, 9, 1, 3, 2, 5, 8 } };

    /** inv: inverse table */
    private static final int[] INV_TABLE = new int[] { 0, 4, 3, 2, 1, 5, 6, 7, 8, 9 };

    /**
     * Validate the Verhoeff <i>Check Digit</i> for a code.
     * 
     * @param code The code to validate
     * @return <code>true</code> if the check digit is valid,
     *         otherwise <code>false</code>
     */
    @Override
    public boolean isValid(String code) {
        if (code == null || code.length() == 0) {
            return false;
        }
        try {
            return (calculateChecksum(code, true) == 0);
        } catch (CheckDigitException e) {
            return false;
        }
    }

    /**
     * Calculate a Verhoeff <i>Check Digit</i> for a code.
     * 
     * @param code The code to calculate the Check Digit for
     * @return The calculated Check Digit
     * @throws CheckDigitException if an error occurs calculating
     *             the check digit for the specified code
     */
    @Override
    public String calculate(String code) throws CheckDigitException {
        if (code == null || code.length() == 0) {
            throw new CheckDigitException("Code is missing");
        }
        int checksum = calculateChecksum(code, false);
        return Integer.toString(INV_TABLE[checksum]);
    }

    /**
     * Calculate the checksum.
     * 
     * @param code The code to calculate the checksum for.
     * @param includesCheckDigit Whether the code includes the Check Digit or not.
     * @return The checksum value
     * @throws CheckDigitException if the code contains an invalid character (i.e. not numeric)
     */
    private int calculateChecksum(String code, boolean includesCheckDigit) throws CheckDigitException {
        int checksum = 0;
        for (int i = 0; i < code.length(); i++) {
            int idx = code.length() - (i + 1);
            int num = Character.getNumericValue(code.charAt(idx));
            if (num < 0 || num > 9) {
                throw new CheckDigitException("Invalid Character[" + i + "] = '" + ((int) code.charAt(idx)) + "'");
            }
            int pos = includesCheckDigit ? i : i + 1;
            checksum = D_TABLE[checksum][P_TABLE[pos % 8][num]];
        }
        return checksum;
    }

}