/*
* 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.nl;
import java.io.IOException;
import java.io.Reader;
import java.nio.charset.StandardCharsets;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.CharArrayMap;
import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.StopFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.WordlistLoader;
import org.apache.lucene.analysis.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.miscellaneous.StemmerOverrideFilter.StemmerOverrideMap;
import org.apache.lucene.analysis.miscellaneous.StemmerOverrideFilter;
import org.apache.lucene.analysis.snowball.SnowballFilter;
import org.apache.lucene.analysis.standard.StandardFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.CharsRefBuilder;
import org.apache.lucene.util.IOUtils;
/**
* {@link Analyzer} for Dutch language.
* <p>
* Supports an external list of stopwords (words that
* will not be indexed at all), an external list of exclusions (word that will
* not be stemmed, but indexed) and an external list of word-stem pairs that overrule
* the algorithm (dictionary stemming).
* A default set of stopwords is used unless an alternative list is specified, but the
* exclusion list is empty by default.
* </p>
*/
// TODO: extend StopwordAnalyzerBase
public final class DutchAnalyzer extends Analyzer {
/** File containing default Dutch stopwords. */
public final static String DEFAULT_STOPWORD_FILE = "dutch_stop.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;
}
private static class DefaultSetHolder {
static final CharArraySet DEFAULT_STOP_SET;
static final CharArrayMap<String> DEFAULT_STEM_DICT;
static {
try {
DEFAULT_STOP_SET = WordlistLoader.getSnowballWordSet(IOUtils.getDecodingReader(SnowballFilter.class,
DEFAULT_STOPWORD_FILE, StandardCharsets.UTF_8));
} 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");
}
DEFAULT_STEM_DICT = new CharArrayMap<>(4, false);
DEFAULT_STEM_DICT.put("fiets", "fiets"); //otherwise fiet
DEFAULT_STEM_DICT.put("bromfiets", "bromfiets"); //otherwise bromfiet
DEFAULT_STEM_DICT.put("ei", "eier");
DEFAULT_STEM_DICT.put("kind", "kinder");
}
}
/**
* Contains the stopwords used with the StopFilter.
*/
private final CharArraySet stoptable;
/**
* Contains words that should be indexed but not stemmed.
*/
private CharArraySet excltable = CharArraySet.EMPTY_SET;
private final StemmerOverrideMap stemdict;
/**
* Builds an analyzer with the default stop words ({@link #getDefaultStopSet()})
* and a few default entries for the stem exclusion table.
*
*/
public DutchAnalyzer() {
this(DefaultSetHolder.DEFAULT_STOP_SET, CharArraySet.EMPTY_SET, DefaultSetHolder.DEFAULT_STEM_DICT);
}
public DutchAnalyzer(CharArraySet stopwords){
this(stopwords, CharArraySet.EMPTY_SET, DefaultSetHolder.DEFAULT_STEM_DICT);
}
public DutchAnalyzer(CharArraySet stopwords, CharArraySet stemExclusionTable){
this(stopwords, stemExclusionTable, DefaultSetHolder.DEFAULT_STEM_DICT);
}
public DutchAnalyzer(CharArraySet stopwords, CharArraySet stemExclusionTable, CharArrayMap<String> stemOverrideDict) {
this.stoptable = CharArraySet.unmodifiableSet(CharArraySet.copy(stopwords));
this.excltable = CharArraySet.unmodifiableSet(CharArraySet.copy(stemExclusionTable));
if (stemOverrideDict.isEmpty()) {
this.stemdict = null;
} else {
// we don't need to ignore case here since we lowercase in this analyzer anyway
StemmerOverrideFilter.Builder builder = new StemmerOverrideFilter.Builder(false);
CharArrayMap<String>.EntryIterator iter = stemOverrideDict.entrySet().iterator();
CharsRefBuilder spare = new CharsRefBuilder();
while (iter.hasNext()) {
char[] nextKey = iter.nextKey();
spare.copyChars(nextKey, 0, nextKey.length);
builder.add(spare.get(), iter.currentValue());
}
try {
this.stemdict = builder.build();
} catch (IOException ex) {
throw new RuntimeException("can not build stem dict", ex);
}
}
}
/**
* Returns a (possibly reused) {@link TokenStream} which tokenizes all the
* text in the provided {@link Reader}.
*
* @return A {@link TokenStream} built from a {@link StandardTokenizer}
* filtered with {@link StandardFilter}, {@link LowerCaseFilter},
* {@link StopFilter}, {@link SetKeywordMarkerFilter} if a stem exclusion set is provided,
* {@link StemmerOverrideFilter}, and {@link SnowballFilter}
*/
@Override
protected TokenStreamComponents createComponents(String fieldName) {
final Tokenizer source = new StandardTokenizer();
TokenStream result = new StandardFilter(source);
result = new LowerCaseFilter(result);
result = new StopFilter(result, stoptable);
if (!excltable.isEmpty())
result = new SetKeywordMarkerFilter(result, excltable);
if (stemdict != null)
result = new StemmerOverrideFilter(result, stemdict);
result = new SnowballFilter(result, new org.tartarus.snowball.ext.DutchStemmer());
return new TokenStreamComponents(source, result);
}
@Override
protected TokenStream normalize(String fieldName, TokenStream in) {
TokenStream result = new StandardFilter(in);
result = new LowerCaseFilter(result);
return result;
}
}