Lucene example source code file (PersianAnalyzer.java)

This example Lucene source code file (PersianAnalyzer.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

default_stop_set, deprecated, io, ioexception, override, persiananalyzer, persiananalyzer, reader, set, set, stopwords_comment, stopwords_comment, string, string, tokenstreamcomponents, util

The Lucene PersianAnalyzer.java source code

package org.apache.lucene.analysis.fa;

/**
 * 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.StopFilter;
import org.apache.lucene.analysis.StopwordAnalyzerBase;
import org.apache.lucene.analysis.CharReader;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.WordlistLoader;
import org.apache.lucene.analysis.ar.ArabicLetterTokenizer;
import org.apache.lucene.analysis.ar.ArabicNormalizationFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;

import org.apache.lucene.util.Version;

/**
 * {@link Analyzer} for Persian.
 * <p>
 * This Analyzer uses {@link ArabicLetterTokenizer} which implies tokenizing around
 * zero-width non-joiner in addition to whitespace. Some persian-specific variant forms (such as farsi
 * yeh and keheh) are standardized. "Stemming" is accomplished via stopwords.
 * </p>
 */
public final class PersianAnalyzer extends StopwordAnalyzerBase {

  /**
   * File containing default Persian 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
   */
  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, PersianAnalyzer.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");
      }
    }
  }

  /**
   * Builds an analyzer with the default stop words:
   * {@link #DEFAULT_STOPWORD_FILE}.
   */
  public PersianAnalyzer(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 PersianAnalyzer(Version matchVersion, Set<?> stopwords){
    super(matchVersion, stopwords);
  }

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

  /**
   * Builds an analyzer with the given stop words.
   * @deprecated use {@link #PersianAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public PersianAnalyzer(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 #PersianAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public PersianAnalyzer(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 a {@link StandardTokenizer} filtered with
   *         {@link LowerCaseFilter}, {@link ArabicNormalizationFilter},
   *         {@link PersianNormalizationFilter} and Persian Stop words
   */
  @Override
  protected TokenStreamComponents createComponents(String fieldName,
      Reader reader) {
    final Tokenizer source;
    if (matchVersion.onOrAfter(Version.LUCENE_31)) {
      source = new StandardTokenizer(matchVersion, reader);
    } else {
      source = new ArabicLetterTokenizer(matchVersion, reader);
    }
    TokenStream result = new LowerCaseFilter(matchVersion, source);
    result = new ArabicNormalizationFilter(result);
    /* additional persian-specific normalization */
    result = new PersianNormalizationFilter(result);
    /*
     * the order here is important: the stopword list is normalized with the
     * above!
     */
    return new TokenStreamComponents(source, new StopFilter(matchVersion, result, stopwords));
  }
  
  /** 
   * Wraps the Reader with {@link PersianCharFilter}
   */
  @Override
  protected Reader initReader(Reader reader) {
    return matchVersion.onOrAfter(Version.LUCENE_31) ? 
       new PersianCharFilter(CharReader.get(reader)) :
       reader;
  }
}