org.apache.lucene.analysis.fa.PersianAnalyzer Maven / Gradle / Ivy
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/*
* 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.
*/
package org.apache.lucene.analysis.fa;
import java.io.IOException;
import java.io.Reader;
import java.io.UncheckedIOException;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.LowerCaseFilter;
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.ar.ArabicNormalizationFilter;
import org.apache.lucene.analysis.core.DecimalDigitFilter;
import org.apache.lucene.analysis.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.IOUtils;
/**
* {@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.
*
* @since 3.1
*/
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 static final 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 =
WordlistLoader.getWordSet(
IOUtils.requireResourceNonNull(
PersianAnalyzer.class.getResourceAsStream(DEFAULT_STOPWORD_FILE),
DEFAULT_STOPWORD_FILE),
STOPWORDS_COMMENT);
} catch (IOException ex) {
// default set should always be present as it is part of the
// distribution (JAR)
throw new UncheckedIOException("Unable to load default stopword set", ex);
}
}
}
private final CharArraySet stemExclusionSet;
/** Builds an analyzer with the default stop words: {@link #DEFAULT_STOPWORD_FILE}. */
public PersianAnalyzer() {
this(DefaultSetHolder.DEFAULT_STOP_SET);
}
/**
* Builds an analyzer with the given stop words
*
* @param stopwords a stopword set
*/
public PersianAnalyzer(CharArraySet stopwords) {
this(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 SetKeywordMarkerFilter} before {@link PersianStemFilter}.
*
* @param stopwords a stopword set
* @param stemExclusionSet a set of terms not to be stemmed
*/
public PersianAnalyzer(CharArraySet stopwords, CharArraySet stemExclusionSet) {
super(stopwords);
this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(stemExclusionSet));
}
/**
* 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 DecimalDigitFilter},
* {@link ArabicNormalizationFilter}, {@link PersianNormalizationFilter}, Persian Stop words,
* and {@link PersianStemFilter}.
*/
@Override
protected TokenStreamComponents createComponents(String fieldName) {
final Tokenizer source = new StandardTokenizer();
TokenStream result = new LowerCaseFilter(source);
result = new DecimalDigitFilter(result);
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!
*/
result = new StopFilter(result, stopwords);
if (!stemExclusionSet.isEmpty()) {
result = new SetKeywordMarkerFilter(result, stemExclusionSet);
}
return new TokenStreamComponents(source, new PersianStemFilter(result));
}
@Override
protected TokenStream normalize(String fieldName, TokenStream in) {
TokenStream result = new LowerCaseFilter(in);
result = new DecimalDigitFilter(result);
result = new ArabicNormalizationFilter(result);
/* additional persian-specific normalization */
result = new PersianNormalizationFilter(result);
return result;
}
/** Wraps the Reader with {@link PersianCharFilter} */
@Override
protected Reader initReader(String fieldName, Reader reader) {
return new PersianCharFilter(reader);
}
}