package org.apache.lucene.analysis.cz;
/*
* 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 org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.core.LowerCaseFilter;
import org.apache.lucene.analysis.core.StopFilter;
import org.apache.lucene.analysis.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.standard.StandardFilter;
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.analysis.util.WordlistLoader;
import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.Version;
import java.io.*;
import java.nio.charset.StandardCharsets;
/**
* {@link Analyzer} for Czech language.
* <p>
* Supports an external list of stopwords (words that will not be indexed at
* all). A default set of stopwords is used unless an alternative list is
* specified.
* </p>
*
* <a name="version"/>
* <p>
* You must specify the required {@link Version} compatibility when creating
* CzechAnalyzer:
* <ul>
* <li>As of 3.1, words are stemmed with {@link CzechStemFilter}
* <li>As of 2.9, StopFilter preserves position increments
* <li>As of 2.4, Tokens incorrectly identified as acronyms are corrected (see
* <a href="https://issues.apache.org/jira/browse/LUCENE-1068">LUCENE-1068</a>)
* </ul>
*/
public final class CzechAnalyzer extends StopwordAnalyzerBase {
/** File containing default Czech stopwords. */
public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";
/**
* Returns a set of default Czech-stopwords
*
* @return a set of default Czech-stopwords
*/
public static final CharArraySet getDefaultStopSet(){
return DefaultSetHolder.DEFAULT_SET;
}
private static class DefaultSetHolder {
private static final CharArraySet DEFAULT_SET;
static {
try {
DEFAULT_SET = WordlistLoader.getWordSet(IOUtils.getDecodingReader(CzechAnalyzer.class,
DEFAULT_STOPWORD_FILE, StandardCharsets.UTF_8), "#", Version.LUCENE_CURRENT);
} 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 CharArraySet stemExclusionTable;
/**
* Builds an analyzer with the default stop words ({@link #getDefaultStopSet()}).
*
* @param matchVersion Lucene version to match See
* {@link <a href="#version">above</a>}
*/
public CzechAnalyzer(Version matchVersion) {
this(matchVersion, DefaultSetHolder.DEFAULT_SET);
}
/**
* Builds an analyzer with the given stop words.
*
* @param matchVersion Lucene version to match See
* {@link <a href="#version">above</a>}
* @param stopwords a stopword set
*/
public CzechAnalyzer(Version matchVersion, CharArraySet stopwords) {
this(matchVersion, stopwords, CharArraySet.EMPTY_SET);
}
/**
* Builds an analyzer with the given stop words and a set of work to be
* excluded from the {@link CzechStemFilter}.
*
* @param matchVersion Lucene version to match See
* {@link <a href="#version">above</a>}
* @param stopwords a stopword set
* @param stemExclusionTable a stemming exclusion set
*/
public CzechAnalyzer(Version matchVersion, CharArraySet stopwords, CharArraySet stemExclusionTable) {
super(matchVersion, stopwords);
this.stemExclusionTable = CharArraySet.unmodifiableSet(CharArraySet.copy(matchVersion, stemExclusionTable));
}
/**
* 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 StandardFilter}, {@link LowerCaseFilter}, {@link StopFilter}
* , and {@link CzechStemFilter} (only if version is >= LUCENE_3_1). If
* a version is >= LUCENE_3_1 and a stem exclusion set is provided via
* {@link #CzechAnalyzer(Version, CharArraySet, CharArraySet)} a
* {@link SetKeywordMarkerFilter} is added before
* {@link CzechStemFilter}.
*/
@Override
protected 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 (matchVersion.onOrAfter(Version.LUCENE_3_1)) {
if(!this.stemExclusionTable.isEmpty())
result = new SetKeywordMarkerFilter(result, stemExclusionTable);
result = new CzechStemFilter(result);
}
return new TokenStreamComponents(source, result);
}
}