Apache Commons Codec library provides implementations of common encoders and decoders such as Base64, Hex, Phonetic and URLs.

Apache Commons Codec Source Code files are provided in both binary packge (commons-codec-3.15-bin.zip) and source package (commons-codec-3.15-src.zip). You can download them at Apache Commons Codec Website.

Apache Commons Codec Source Code has no dependencies. You can compile it to generate your own version of Apache Commons Codec JAR file.

The source code of Apache Commons Codec 1.15 is provided below:

⏎ org/apache/commons/codec/language/ColognePhonetic.java

/*
 * 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.codec.language;

import java.util.Locale;

import org.apache.commons.codec.EncoderException;
import org.apache.commons.codec.StringEncoder;

/**
 * Encodes a string into a Cologne Phonetic value.
 * <p>
 * Implements the <a href="http://de.wikipedia.org/wiki/K%C3%B6lner_Phonetik">K&ouml;lner Phonetik</a> (Cologne
 * Phonetic) algorithm issued by Hans Joachim Postel in 1969.
 * </p>
 * <p>
 * The <i>K&ouml;lner Phonetik</i> is a phonetic algorithm which is optimized for the German language. It is related to
 * the well-known soundex algorithm.
 * </p>
 *
 * <h2>Algorithm</h2>
 *
 * <ul>
 *
 * <li>
 * <h3>Step 1:</h3>
 * After preprocessing (conversion to upper case, transcription of <a
 * href="http://en.wikipedia.org/wiki/Germanic_umlaut">germanic umlauts</a>, removal of non alphabetical characters) the
 * letters of the supplied text are replaced by their phonetic code according to the following table.
 * <table border="1">
 * <caption style="caption-side: bottom"><small><i>(Source: <a
 * href="http://de.wikipedia.org/wiki/K%C3%B6lner_Phonetik#Buchstabencodes">Wikipedia (de): K&ouml;lner Phonetik --
 * Buchstabencodes</a>)</i></small></caption> <tbody>
 * <tr>
 * <th>Letter</th>
 * <th>Context</th>
 * <th>Code</th>
 * </tr>
 * <tr>
 * <td>A, E, I, J, O, U, Y</td>
 * <td></td>
 * <td>0</td>
 * </tr>
 * <tr>
 *
 * <td>H</td>
 * <td></td>
 * <td>-</td>
 * </tr>
 * <tr>
 * <td>B</td>
 * <td></td>
 * <td rowspan="2">1</td>
 * </tr>
 * <tr>
 * <td>P</td>
 * <td>not before H</td>
 *
 * </tr>
 * <tr>
 * <td>D, T</td>
 * <td>not before C, S, Z</td>
 * <td>2</td>
 * </tr>
 * <tr>
 * <td>F, V, W</td>
 * <td></td>
 * <td rowspan="2">3</td>
 * </tr>
 * <tr>
 *
 * <td>P</td>
 * <td>before H</td>
 * </tr>
 * <tr>
 * <td>G, K, Q</td>
 * <td></td>
 * <td rowspan="3">4</td>
 * </tr>
 * <tr>
 * <td rowspan="2">C</td>
 * <td>at onset before A, H, K, L, O, Q, R, U, X</td>
 *
 * </tr>
 * <tr>
 * <td>before A, H, K, O, Q, U, X except after S, Z</td>
 * </tr>
 * <tr>
 * <td>X</td>
 * <td>not after C, K, Q</td>
 * <td>48</td>
 * </tr>
 * <tr>
 * <td>L</td>
 * <td></td>
 *
 * <td>5</td>
 * </tr>
 * <tr>
 * <td>M, N</td>
 * <td></td>
 * <td>6</td>
 * </tr>
 * <tr>
 * <td>R</td>
 * <td></td>
 * <td>7</td>
 * </tr>
 *
 * <tr>
 * <td>S, Z</td>
 * <td></td>
 * <td rowspan="6">8</td>
 * </tr>
 * <tr>
 * <td rowspan="3">C</td>
 * <td>after S, Z</td>
 * </tr>
 * <tr>
 * <td>at onset except before A, H, K, L, O, Q, R, U, X</td>
 * </tr>
 *
 * <tr>
 * <td>not before A, H, K, O, Q, U, X</td>
 * </tr>
 * <tr>
 * <td>D, T</td>
 * <td>before C, S, Z</td>
 * </tr>
 * <tr>
 * <td>X</td>
 * <td>after C, K, Q</td>
 * </tr>
 * </tbody>
 * </table>
 *
 * <h4>Example:</h4>
 *
 * {@code "M}&uuml;{@code ller-L}&uuml;<code>denscheidt"
 * =&gt; "MULLERLUDENSCHEIDT" =&gt; "6005507500206880022"</code>
 *
 * </li>
 *
 * <li>
 * <h3>Step 2:</h3>
 * Collapse of all multiple consecutive code digits.
 * <h4>Example:</h4>
 * {@code "6005507500206880022" =&gt; "6050750206802"}</li>
 *
 * <li>
 * <h3>Step 3:</h3>
 * Removal of all codes "0" except at the beginning. This means that two or more identical consecutive digits can occur
 * if they occur after removing the "0" digits.
 *
 * <h4>Example:</h4>
 * {@code "6050750206802" =&gt; "65752682"}</li>
 *
 * </ul>
 *
 * <p>
 * This class is thread-safe.
 * </p>
 *
 * @see <a href="http://de.wikipedia.org/wiki/K%C3%B6lner_Phonetik">Wikipedia (de): K&ouml;lner Phonetik (in German)</a>
 * @since 1.5
 */
public class ColognePhonetic implements StringEncoder {

    // Predefined char arrays for better performance and less GC load
    private static final char[] AEIJOUY = new char[] { 'A', 'E', 'I', 'J', 'O', 'U', 'Y' };
    private static final char[] CSZ = new char[] { 'C', 'S', 'Z' };
    private static final char[] FPVW = new char[] { 'F', 'P', 'V', 'W' };
    private static final char[] GKQ = new char[] { 'G', 'K', 'Q' };
    private static final char[] CKQ = new char[] { 'C', 'K', 'Q' };
    private static final char[] AHKLOQRUX = new char[] { 'A', 'H', 'K', 'L', 'O', 'Q', 'R', 'U', 'X' };
    private static final char[] SZ = new char[] { 'S', 'Z' };
    private static final char[] AHKOQUX = new char[] { 'A', 'H', 'K', 'O', 'Q', 'U', 'X' };
    private static final char[] DTX = new char[] { 'D', 'T', 'X' };

    private static final char CHAR_IGNORE = '-';    // is this character to be ignored?

    /**
     * This class is not thread-safe; the field {@link #length} is mutable.
     * However, it is not shared between threads, as it is constructed on demand
     * by the method {@link ColognePhonetic#colognePhonetic(String)}
     */
    private abstract class CologneBuffer {

        protected final char[] data;

        protected int length = 0;

        public CologneBuffer(final char[] data) {
            this.data = data;
            this.length = data.length;
        }

        public CologneBuffer(final int buffSize) {
            this.data = new char[buffSize];
            this.length = 0;
        }

        protected abstract char[] copyData(int start, final int length);

        public int length() {
            return length;
        }

        @Override
        public String toString() {
            return new String(copyData(0, length));
        }
    }

    private class CologneOutputBuffer extends CologneBuffer {

        private char lastCode;

        public CologneOutputBuffer(final int buffSize) {
            super(buffSize);
            lastCode = '/'; // impossible value
        }

        /**
         * Stores the next code in the output buffer, keeping track of the previous code.
         * '0' is only stored if it is the first entry.
         * Ignored chars are never stored.
         * If the code is the same as the last code (whether stored or not) it is not stored.
         *
         * @param code the code to store.
         */
        public void put(final char code) {
            if (code != CHAR_IGNORE && lastCode != code && (code != '0' || length == 0)) {
                data[length] = code;
                length++;
            }
            lastCode = code;
        }

        @Override
        protected char[] copyData(final int start, final int length) {
            final char[] newData = new char[length];
            System.arraycopy(data, start, newData, 0, length);
            return newData;
        }
    }

    private class CologneInputBuffer extends CologneBuffer {

        public CologneInputBuffer(final char[] data) {
            super(data);
        }

        @Override
        protected char[] copyData(final int start, final int length) {
            final char[] newData = new char[length];
            System.arraycopy(data, data.length - this.length + start, newData, 0, length);
            return newData;
        }

        public char getNextChar() {
            return data[getNextPos()];
        }

        protected int getNextPos() {
            return data.length - length;
        }

        public char removeNext() {
            final char ch = getNextChar();
            length--;
            return ch;
        }
    }

    /*
     * Returns whether the array contains the key, or not.
     */
    private static boolean arrayContains(final char[] arr, final char key) {
        for (final char element : arr) {
            if (element == key) {
                return true;
            }
        }
        return false;
    }

    /**
     * <p>
     * Implements the <i>K&ouml;lner Phonetik</i> algorithm.
     * </p>
     * <p>
     * In contrast to the initial description of the algorithm, this implementation does the encoding in one pass.
     * </p>
     *
     * @param text The source text to encode
     * @return the corresponding encoding according to the <i>K&ouml;lner Phonetik</i> algorithm
     */
    public String colognePhonetic(final String text) {
        if (text == null) {
            return null;
        }

        final CologneInputBuffer input = new CologneInputBuffer(preprocess(text));
        final CologneOutputBuffer output = new CologneOutputBuffer(input.length() * 2);

        char nextChar;

        char lastChar = CHAR_IGNORE;
        char chr;

        while (input.length() > 0) {
            chr = input.removeNext();

            if (input.length() > 0) {
                nextChar = input.getNextChar();
            } else {
                nextChar = CHAR_IGNORE;
            }

            if (chr < 'A' || chr > 'Z') {
                    continue; // ignore unwanted characters
            }

            if (arrayContains(AEIJOUY, chr)) {
                output.put('0');
            } else if (chr == 'B' || (chr == 'P' && nextChar != 'H')) {
                output.put('1');
            } else if ((chr == 'D' || chr == 'T') && !arrayContains(CSZ, nextChar)) {
                output.put('2');
            } else if (arrayContains(FPVW, chr)) {
                output.put('3');
            } else if (arrayContains(GKQ, chr)) {
                output.put('4');
            } else if (chr == 'X' && !arrayContains(CKQ, lastChar)) {
                output.put('4');
                output.put('8');
            } else if (chr == 'S' || chr == 'Z') {
                output.put('8');
            } else if (chr == 'C') {
                if (output.length() == 0) {
                    if (arrayContains(AHKLOQRUX, nextChar)) {
                        output.put('4');
                    } else {
                        output.put('8');
                    }
                } else {
                    if (arrayContains(SZ, lastChar) || !arrayContains(AHKOQUX, nextChar)) {
                        output.put('8');
                    } else {
                        output.put('4');
                    }
                }
            } else if (arrayContains(DTX, chr)) {
                output.put('8');
            } else if (chr == 'R') {
                output.put('7');
            } else if (chr == 'L') {
                output.put('5');
            } else if (chr == 'M' || chr == 'N') {
                output.put('6');
            } else if (chr == 'H') {
                output.put(CHAR_IGNORE); // needed by put
            } else {
                // ignored; should not happen
            }

            lastChar = chr;
        }
        return output.toString();
    }

    @Override
    public Object encode(final Object object) throws EncoderException {
        if (!(object instanceof String)) {
            throw new EncoderException("This method's parameter was expected to be of the type " +
                String.class.getName() +
                ". But actually it was of the type " +
                object.getClass().getName() +
                ".");
        }
        return encode((String) object);
    }

    @Override
    public String encode(final String text) {
        return colognePhonetic(text);
    }

    /**
     * Compares the first encoded string to the second encoded string.
     *
     * @param text1 source text to encode before testing for equality.
     * @param text2 source text to encode before testing for equality.
     * @return {@code true} if the encoding the first string equals the encoding of the second string, {@code false}
     *         otherwise
     */
    public boolean isEncodeEqual(final String text1, final String text2) {
        return colognePhonetic(text1).equals(colognePhonetic(text2));
    }

    /**
     * Converts the string to upper case and replaces Germanic umlaut characters
     * The following characters are mapped:
     * <ul>
     * <li>capital A, umlaut mark</li>
     * <li>capital U, umlaut mark</li>
     * <li>capital O, umlaut mark</li>
     * <li>small sharp s, German</li>
     * </ul>
     */
    private char[] preprocess(final String text) {
        // This converts German small sharp s (Eszett) to SS
        final char[] chrs = text.toUpperCase(Locale.GERMAN).toCharArray();

        for (int index = 0; index < chrs.length; index++) {
            switch (chrs[index]) {
                case '\u00C4': // capital A, umlaut mark
                    chrs[index] = 'A';
                    break;
                case '\u00DC': // capital U, umlaut mark
                    chrs[index] = 'U';
                    break;
                case '\u00D6': // capital O, umlaut mark
                    chrs[index] = 'O';
                    break;
                default:
                    break;
            }
        }
        return chrs;
    }
}

⏎ org/apache/commons/codec/language/ColognePhonetic.java

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Release date: 2020-09-01
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