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Lucene example source code file (ArabicAnalyzer.java)

This example Lucene source code file (ArabicAnalyzer.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

arabicanalyzer, arabicanalyzer, default_stop_set, default_stopword_file, deprecated, deprecated, io, ioexception, set, set, stopwords_comment, stopwords_comment, string, tokenstreamcomponents, util, version

The Lucene ArabicAnalyzer.java source code

package org.apache.lucene.analysis.ar;

/**
 * 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 java.io.File;
import java.io.IOException;
import java.io.Reader;
import java.util.Hashtable;
import java.util.Set;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.KeywordMarkerFilter;
import org.apache.lucene.analysis.StopFilter;
import org.apache.lucene.analysis.StopwordAnalyzerBase;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.WordlistLoader;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.Version;

/**
 * {@link Analyzer} for Arabic. 
 * <p>
 * This analyzer implements light-stemming as specified by:
 * <i>
 * Light Stemming for Arabic Information Retrieval
 * </i>    
 * http://www.mtholyoke.edu/~lballest/Pubs/arab_stem05.pdf
 * <p>
 * The analysis package contains three primary components:
 * <ul>
 *  <li>{@link ArabicNormalizationFilter}: Arabic orthographic normalization.
 *  <li>{@link ArabicStemFilter}: Arabic light stemming
 *  <li>Arabic stop words file: a set of default Arabic stop words.
 * </ul>
 * 
 */
public final class ArabicAnalyzer extends StopwordAnalyzerBase {

  /**
   * File containing default Arabic stopwords.
   * 
   * Default stopword list is from http://members.unine.ch/jacques.savoy/clef/index.html
   * The stopword list is BSD-Licensed.
   */
  public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";

  /**
   * The comment character in the stopwords file.  All lines prefixed with this will be ignored
   * @deprecated use {@link WordlistLoader#getWordSet(File, String)} directly  
   */
  // TODO make this private 
  @Deprecated
  public static final String STOPWORDS_COMMENT = "#";
  
  /**
   * Returns an unmodifiable instance of the default stop-words set.
   * @return an unmodifiable instance of the default stop-words set.
   */
  public static Set<?> getDefaultStopSet(){
    return DefaultSetHolder.DEFAULT_STOP_SET;
  }
  
  /**
   * Atomically loads the DEFAULT_STOP_SET in a lazy fashion once the outer class 
   * accesses the static final set the first time.;
   */
  private static class DefaultSetHolder {
    static final Set<?> DEFAULT_STOP_SET;

    static {
      try {
        DEFAULT_STOP_SET = loadStopwordSet(false, ArabicAnalyzer.class, DEFAULT_STOPWORD_FILE, STOPWORDS_COMMENT);
      } catch (IOException ex) {
        // default set should always be present as it is part of the
        // distribution (JAR)
        throw new RuntimeException("Unable to load default stopword set");
      }
    }
  }
  
  private final Set<?> stemExclusionSet;

  /**
   * Builds an analyzer with the default stop words: {@link #DEFAULT_STOPWORD_FILE}.
   */
  public ArabicAnalyzer(Version matchVersion) {
    this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET);
  }
  
  /**
   * Builds an analyzer with the given stop words
   * 
   * @param matchVersion
   *          lucene compatibility version
   * @param stopwords
   *          a stopword set
   */
  public ArabicAnalyzer(Version matchVersion, Set<?> stopwords){
    this(matchVersion, stopwords, CharArraySet.EMPTY_SET);
  }

  /**
   * Builds an analyzer with the given stop word. If a none-empty stem exclusion set is
   * provided this analyzer will add a {@link KeywordMarkerFilter} before
   * {@link ArabicStemFilter}.
   * 
   * @param matchVersion
   *          lucene compatibility version
   * @param stopwords
   *          a stopword set
   * @param stemExclusionSet
   *          a set of terms not to be stemmed
   */
  public ArabicAnalyzer(Version matchVersion, Set<?> stopwords, Set stemExclusionSet){
    super(matchVersion, stopwords);
    this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(
        matchVersion, stemExclusionSet));
  }

  /**
   * Builds an analyzer with the given stop words.
   * @deprecated use {@link #ArabicAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public ArabicAnalyzer( Version matchVersion, String... stopwords ) {
    this(matchVersion, StopFilter.makeStopSet(matchVersion, stopwords ));
  }

  /**
   * Builds an analyzer with the given stop words.
   * @deprecated use {@link #ArabicAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public ArabicAnalyzer( Version matchVersion, Hashtable<?,?> stopwords ) {
    this(matchVersion, stopwords.keySet());
  }

  /**
   * Builds an analyzer with the given stop words.  Lines can be commented out using {@link #STOPWORDS_COMMENT}
   * @deprecated use {@link #ArabicAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public ArabicAnalyzer( Version matchVersion, File stopwords ) throws IOException {
    this(matchVersion, WordlistLoader.getWordSet( stopwords, STOPWORDS_COMMENT));
  }

  /**
   * Creates
   * {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
   * used to tokenize all the text in the provided {@link Reader}.
   * 
   * @return {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
   *         built from an {@link StandardTokenizer} filtered with
   *         {@link LowerCaseFilter}, {@link StopFilter},
   *         {@link ArabicNormalizationFilter}, {@link KeywordMarkerFilter}
   *         if a stem exclusion set is provided and {@link ArabicStemFilter}.
   */
  @Override
  protected TokenStreamComponents createComponents(String fieldName,
      Reader reader) {
    final Tokenizer source = matchVersion.onOrAfter(Version.LUCENE_31) ? 
        new StandardTokenizer(matchVersion, reader) : new ArabicLetterTokenizer(matchVersion, reader);
    TokenStream result = new LowerCaseFilter(matchVersion, source);
    // the order here is important: the stopword list is not normalized!
    result = new StopFilter( matchVersion, result, stopwords);
    // TODO maybe we should make ArabicNormalization filter also KeywordAttribute aware?!
    result = new ArabicNormalizationFilter(result);
    if(!stemExclusionSet.isEmpty()) {
      result = new KeywordMarkerFilter(result, stemExclusionSet);
    }
    return new TokenStreamComponents(source, new ArabicStemFilter(result));
  }
}

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