org.apache.lucene.analysis.fa.PersianAnalyzer Maven / Gradle / Ivy
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.IOException;
import java.io.Reader;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.ar.ArabicLetterTokenizer;
import org.apache.lucene.analysis.ar.ArabicNormalizationFilter;
import org.apache.lucene.analysis.core.LowerCaseFilter;
import org.apache.lucene.analysis.core.StopFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.analysis.util.CharArraySet;
import org.apache.lucene.analysis.util.StopwordAnalyzerBase;
import org.apache.lucene.util.Version;
/**
* {@link Analyzer} for Persian.
*
* This Analyzer uses {@link PersianCharFilter} 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.
*
*/
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 CharArraySet 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 CharArraySet 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, CharArraySet stopwords){
super(matchVersion, stopwords);
}
/**
* Creates
* {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents}
* used to tokenize all the text in the provided {@link Reader}.
*
* @return {@link org.apache.lucene.analysis.Analyzer.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_3_1)) {
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(String fieldName, Reader reader) {
return matchVersion.onOrAfter(Version.LUCENE_3_1) ?
new PersianCharFilter(reader) :
reader;
}
}