org.apache.lucene.analysis.bg.BulgarianAnalyzer Maven / Gradle / Ivy
package org.apache.lucene.analysis.bg;
/**
* 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.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.StandardFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.Version;
/**
* {@link Analyzer} for Bulgarian.
*
* This analyzer implements light-stemming as specified by: Searching
* Strategies for the Bulgarian Language
* http://members.unine.ch/jacques.savoy/Papers/BUIR.pdf
*
*/
public final class BulgarianAnalyzer extends StopwordAnalyzerBase {
/**
* File containing default Bulgarian 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(Reader, String, Version)} 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, BulgarianAnalyzer.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 BulgarianAnalyzer(Version matchVersion) {
this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET);
}
/**
* Builds an analyzer with the given stop words.
*/
public BulgarianAnalyzer(Version matchVersion, Set stopwords) {
this(matchVersion, stopwords, CharArraySet.EMPTY_SET);
}
/**
* Builds an analyzer with the given stop words and a stem exclusion set.
* If a stem exclusion set is provided this analyzer will add a {@link KeywordMarkerFilter}
* before {@link BulgarianStemFilter}.
*/
public BulgarianAnalyzer(Version matchVersion, Set stopwords, Set stemExclusionSet) {
super(matchVersion, stopwords);
this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(
matchVersion, stemExclusionSet)); }
/**
* Creates a
* {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
* which tokenizes all the text in the provided {@link Reader}.
*
* @return A
* {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
* built from an {@link StandardTokenizer} filtered with
* {@link StandardFilter}, {@link LowerCaseFilter}, {@link StopFilter}
* , {@link KeywordMarkerFilter} if a stem exclusion set is
* provided and {@link BulgarianStemFilter}.
*/
@Override
public TokenStreamComponents createComponents(String fieldName, Reader reader) {
final Tokenizer source = new StandardTokenizer(matchVersion, reader);
TokenStream result = new StandardFilter(matchVersion, source);
result = new LowerCaseFilter(matchVersion, result);
result = new StopFilter(matchVersion, result, stopwords);
if(!stemExclusionSet.isEmpty())
result = new KeywordMarkerFilter(result, stemExclusionSet);
result = new BulgarianStemFilter(result);
return new TokenStreamComponents(source, result);
}
}