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Lucene example source code file (BulgarianStemmer.java)

This example Lucene source code file (BulgarianStemmer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

bulgarianstemmer, bulgarianstemmer, n, n

The Lucene BulgarianStemmer.java source code

package org.apache.lucene.analysis.bg;

/**
 * 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.
 */

import static org.apache.lucene.analysis.util.StemmerUtil.*;

/**
 * Light Stemmer for Bulgarian.
 * <p>
 * Implements the algorithm described in:  
 * <i>
 * Searching Strategies for the Bulgarian Language
 * </i>
 * http://members.unine.ch/jacques.savoy/Papers/BUIR.pdf
 */
public class BulgarianStemmer {
  
  /**
   * Stem an input buffer of Bulgarian text.
   * 
   * @param s input buffer
   * @param len length of input buffer
   * @return length of input buffer after normalization
   */
  public int stem(final char s[], int len) {
    if (len < 4) // do not stem
      return len;
    
    if (len > 5 && endsWith(s, len, "ища"))
      return len - 3;
    
    len = removeArticle(s, len);
    len = removePlural(s, len);
    
    if (len > 3) {
      if (endsWith(s, len, "я"))
        len--;
      if (endsWith(s, len, "а") ||
          endsWith(s, len, "о") ||
          endsWith(s, len, "е"))
        len--;
    }
    
    // the rule to rewrite ен -> н is duplicated in the paper.
    // in the perl implementation referenced by the paper, this is fixed.
    // (it is fixed here as well)
    if (len > 4 && endsWith(s, len, "ен")) {
      s[len - 2] = 'н'; // replace with н
      len--;
    }
    
    if (len > 5 && s[len - 2] == 'ъ') {
      s[len - 2] = s[len - 1]; // replace ъN with N
      len--;
    }

    return len;
  }
  
  /**
   * Mainly remove the definite article
   * @param s input buffer
   * @param len length of input buffer
   * @return new stemmed length
   */
  private int removeArticle(final char s[], final int len) {
    if (len > 6 && endsWith(s, len, "ият"))
      return len - 3;
    
    if (len > 5) {
      if (endsWith(s, len, "ът") ||
          endsWith(s, len, "то") ||
          endsWith(s, len, "те") ||
          endsWith(s, len, "та") ||
          endsWith(s, len, "ия"))
        return len - 2;
    }
    
    if (len > 4 && endsWith(s, len, "ят"))
      return len - 2;

    return len;
  }
  
  private int removePlural(final char s[], final int len) {
    if (len > 6) {
      if (endsWith(s, len, "овци"))
        return len - 3; // replace with о
      if (endsWith(s, len, "ове"))
        return len - 3;
      if (endsWith(s, len, "еве")) {
        s[len - 3] = 'й'; // replace with й
        return len - 2;
      }
    }
    
    if (len > 5) {
      if (endsWith(s, len, "ища"))
        return len - 3;
      if (endsWith(s, len, "та"))
        return len - 2;
      if (endsWith(s, len, "ци")) {
        s[len - 2] = 'к'; // replace with к
        return len - 1;
      }
      if (endsWith(s, len, "зи")) {
        s[len - 2] = 'г'; // replace with г
        return len - 1;
      }
      
      if (s[len - 3] == 'е' && s[len - 1] == 'и') {
        s[len - 3] = 'я'; // replace е with я, remove и
        return len - 1;
      }
    }
    
    if (len > 4) {
      if (endsWith(s, len, "си")) {
        s[len - 2] = 'х'; // replace with х
        return len - 1;
      }
      if (endsWith(s, len, "и"))
        return len - 1;
    }
    
    return len;
  }
}

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