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With inspiration from other libraries

There is a newer version: 2.12.15

/**
 * MVEL 2.0
 * Copyright (C) 2007 The Codehaus
 * Mike Brock, Dhanji Prasanna, John Graham, Mark Proctor
 *
 * Licensed 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.mvel2.util;

/**
 * An implementation of Knuth's soundex algorithm.  Used by the soundslike operator.
 */
public class Soundex {

  /* Implements the mapping
  * from: AEHIOUWYBFPVCGJKQSXZDTLMNR
  * to:   00000000111122222222334556
  */
  public static final char[] MAP = {
      //A   B    C    D    E    F    G    H    I    J    K    L    M
      '0', '1', '2', '3', '0', '1', '2', '0', '0', '2', '2', '4', '5',
      //N  O   P   W   R   S   T   U   V   W   X   Y   Z
      '5', '0', '1', '2', '6', '2', '3', '0', '1', '0', '2', '0', '2'
  };

  /**
   * Convert the given String to its Soundex code.
   *
   * @param s input string
   * @return null If the given string can't be mapped to Soundex.
   */
  public static String soundex(String s) {
    char[] ca = s.toUpperCase().toCharArray();

    StringBuilder res = new StringBuilder();
    char c, prev = '?';

    // Main loop: find up to 4 chars that map.
    for (int i = 0; i < ca.length && res.length() < 4 &&
        (c = ca[i]) != ','; i++) {

      // Check to see if the given character is alphabetic.
      // Text is already converted to uppercase. Algorithm
      // only handles ASCII letters, do NOT use Character.isLetter()!
      // Also, skip double letters.
      if (c >= 'A' && c <= 'Z' && c != prev) {
        prev = c;

        char m = MAP[c - 'A'];
        if (m != '0')
          res.append(m);
      }
    }

    if (res.length() == 0)
      return null;

    for (int i = res.length(); i < 4; i++)
      res.append('0');

    return res.toString();
  }
}