org.apache.lucene.analysis.ar.ArabicAnalyzer 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.ar;
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.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 Arabic.
*
* This analyzer implements light-stemming as specified by: Light Stemming for Arabic
* Information Retrieval http://www.mtholyoke.edu/~lballest/Pubs/arab_stem05.pdf
*
*
The analysis package contains three primary components:
*
*
* - {@link ArabicNormalizationFilter}: Arabic orthographic normalization.
*
- {@link ArabicStemFilter}: Arabic light stemming
*
- Arabic stop words file: a set of default Arabic stop words.
*
*
* @since 3.1
*/
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 static final String DEFAULT_STOPWORD_FILE = "stopwords.txt";
/**
* 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(
ArabicAnalyzer.class.getResourceAsStream(DEFAULT_STOPWORD_FILE),
DEFAULT_STOPWORD_FILE),
"#");
} 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 ArabicAnalyzer() {
this(DefaultSetHolder.DEFAULT_STOP_SET);
}
/**
* Builds an analyzer with the given stop words
*
* @param stopwords a stopword set
*/
public ArabicAnalyzer(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 ArabicStemFilter}.
*
* @param stopwords a stopword set
* @param stemExclusionSet a set of terms not to be stemmed
*/
public ArabicAnalyzer(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 an {@link
* StandardTokenizer} filtered with {@link LowerCaseFilter}, {@link DecimalDigitFilter},
* {@link StopFilter}, {@link ArabicNormalizationFilter}, {@link SetKeywordMarkerFilter} if a
* stem exclusion set is provided and {@link ArabicStemFilter}.
*/
@Override
protected TokenStreamComponents createComponents(String fieldName) {
final Tokenizer source = new StandardTokenizer();
TokenStream result = new LowerCaseFilter(source);
result = new DecimalDigitFilter(result);
// the order here is important: the stopword list is not normalized!
result = new StopFilter(result, stopwords);
// TODO maybe we should make ArabicNormalization filter also KeywordAttribute aware?!
result = new ArabicNormalizationFilter(result);
if (!stemExclusionSet.isEmpty()) {
result = new SetKeywordMarkerFilter(result, stemExclusionSet);
}
return new TokenStreamComponents(source, new ArabicStemFilter(result));
}
@Override
protected TokenStream normalize(String fieldName, TokenStream in) {
TokenStream result = new LowerCaseFilter(in);
result = new DecimalDigitFilter(result);
result = new ArabicNormalizationFilter(result);
return result;
}
}