org.apache.lucene.analysis.de.GermanAnalyzer 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.de;
// This file is encoded in UTF-8
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.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.snowball.SnowballFilter;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.IOUtils;
/**
* {@link Analyzer} for German language.
*
* Supports an external list of stopwords (words that will not be indexed at all) and an external
* list of exclusions (word that will not be stemmed, but indexed). A default set of stopwords is
* used unless an alternative list is specified, but the exclusion list is empty by default.
*
*
NOTE: This class uses the same {@link org.apache.lucene.util.Version} dependent
* settings as {@link StandardAnalyzer}.
*
*
NOTE: This class does not decompound nouns, additional data files are needed,
* incompatible with the Apache 2.0 License. You can find these data files and example code for
* decompounding here.
*
* @since 3.1
* @see https://github.com/uschindler/german-decompounder
*/
public final class GermanAnalyzer extends StopwordAnalyzerBase {
/** File containing default German stopwords. */
public static final String DEFAULT_STOPWORD_FILE = "german_stop.txt";
/**
* Returns a set of default German-stopwords
*
* @return a set of default German-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.getSnowballWordSet(
IOUtils.requireResourceNonNull(
SnowballFilter.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);
}
}
}
/** Contains the stopwords used with the {@link StopFilter}. */
/** Contains words that should be indexed but not stemmed. */
private final CharArraySet exclusionSet;
/** Builds an analyzer with the default stop words: {@link #getDefaultStopSet()}. */
public GermanAnalyzer() {
this(DefaultSetHolder.DEFAULT_SET);
}
/**
* Builds an analyzer with the given stop words
*
* @param stopwords a stopword set
*/
public GermanAnalyzer(CharArraySet stopwords) {
this(stopwords, CharArraySet.EMPTY_SET);
}
/**
* Builds an analyzer with the given stop words
*
* @param stopwords a stopword set
* @param stemExclusionSet a stemming exclusion set
*/
public GermanAnalyzer(CharArraySet stopwords, CharArraySet stemExclusionSet) {
super(stopwords);
exclusionSet = 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 StopFilter}, {@link
* SetKeywordMarkerFilter} if a stem exclusion set is provided, {@link
* GermanNormalizationFilter} and {@link GermanLightStemFilter}
*/
@Override
protected TokenStreamComponents createComponents(String fieldName) {
final Tokenizer source = new StandardTokenizer();
TokenStream result = new LowerCaseFilter(source);
result = new StopFilter(result, stopwords);
result = new SetKeywordMarkerFilter(result, exclusionSet);
result = new GermanNormalizationFilter(result);
result = new GermanLightStemFilter(result);
return new TokenStreamComponents(source, result);
}
@Override
protected TokenStream normalize(String fieldName, TokenStream in) {
TokenStream result = new LowerCaseFilter(in);
result = new GermanNormalizationFilter(result);
return result;
}
}