    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 *      https://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 */
    017package org.apache.commons.validator.routines.checkdigit;
    018
    019/**
    020 * International Standard Serial Number (ISSN)
    021 * is an eight-digit serial number used to
    022 * uniquely identify a serial publication.
    023 * <pre>
    024 * The format is:
    025 *
    026 * ISSN dddd-dddC
    027 * where:
    028 * d = decimal digit (0-9)
    029 * C = checksum (0-9 or X)
    030 *
    031 * The checksum is formed by adding the first 7 digits multiplied by
    032 * the position in the entire number (counting from the right).
    033 * For example, abcd-efg would be 8a + 7b + 6c + 5d + 4e +3f +2g.
    034 * The check digit is modulus 11, where the value 10 is represented by 'X'
    035 * For example:
    036 * ISSN 0317-8471
    037 * ISSN 1050-124X
    038 * </pre>
    039 * <p>
    040 * <strong>Note:</strong> This class expects the input to be numeric only,
    041 * with all formatting removed.
    042 * For example:
    043 * </p>
    044 * <pre>
    045 * 03178471
    046 * 1050124X
    047 * </pre>
    048 *
    049 * @since 1.5.0
    050 */
    051public final class ISSNCheckDigit extends ModulusCheckDigit {
    052
    053    private static final long serialVersionUID = 1L;
    054
    055    /** An ISSN is exactly eight characters: seven digits plus the check digit. */
    056    private static final int ISSN_LEN = 8;
    057
    058    /**
    059     * Singleton ISSN Check Digit instance.
    060     */
    061    public static final CheckDigit ISSN_CHECK_DIGIT = new ISSNCheckDigit();
    062
    063    /**
    064     * Creates the instance using a checkdigit modulus of 11.
    065     */
    066    public ISSNCheckDigit() {
    067        super(MODULUS_11);
    068    }
    069
    070    /**
    071     * {@inheritDoc}
    072     *
    073     * <p>
    074     * The {@code 9 - leftPos} weighting gives a ninth character a weight of zero, so an over-length code left the
    075     * trailing characters unweighted and still passed the modulus test (for example every {@code 03178471} + digit
    076     * validated). The length is checked here so only a genuine eight-character ISSN reaches the check digit test.
    077     * </p>
    078     */
    079    @Override
    080    public boolean isValid(final String code) {
    081        return isLength(code, ISSN_LEN) && super.isValid(code);
    082    }
    083
    084    @Override
    085    protected String toCheckDigit(final int charValue) throws CheckDigitException {
    086        if (charValue == 10) { // CHECKSTYLE IGNORE MagicNumber
    087            return "X";
    088        }
    089        return super.toCheckDigit(charValue);
    090    }
    091
    092    @Override
    093    protected int toInt(final char character, final int leftPos, final int rightPos)
    094            throws CheckDigitException {
    095        if (rightPos == 1 && character == 'X') {
    096            return 10; // CHECKSTYLE IGNORE MagicNumber
    097        }
    098        return super.toInt(character, leftPos, rightPos);
    099    }
    100
    101    @Override
    102    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) throws CheckDigitException {
    103        return charValue * (9 - leftPos); // CHECKSTYLE IGNORE MagicNumber
    104    }
    105}