package org.apache.lucene.analysis.de;
// This file is encoded in UTF-8
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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.
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import java.io.IOException;
import java.io.Reader;
import java.util.Arrays;
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.KeywordMarkerFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.snowball.SnowballFilter;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
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 org.tartarus.snowball.ext.German2Stemmer;
/**
* {@link Analyzer} for German language.
* <p>
* 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.
* </p>
*
* <a name="version"/>
* <p>You must specify the required {@link Version}
* compatibility when creating GermanAnalyzer:
* <ul>
* <li> As of 3.6, GermanLightStemFilter is used for less aggressive stemming.
* <li> As of 3.1, Snowball stemming is done with SnowballFilter, and
* Snowball stopwords are used by default.
* <li> As of 2.9, StopFilter preserves position
* increments
* </ul>
*
* <p><b>NOTE</b>: This class uses the same {@link Version}
* dependent settings as {@link StandardAnalyzer}.</p>
*/
public final class GermanAnalyzer extends StopwordAnalyzerBase {
/** @deprecated in 3.1, remove in Lucene 5.0 (index bw compat) */
@Deprecated
private final static String[] GERMAN_STOP_WORDS = {
"einer", "eine", "eines", "einem", "einen",
"der", "die", "das", "dass", "daß",
"du", "er", "sie", "es",
"was", "wer", "wie", "wir",
"und", "oder", "ohne", "mit",
"am", "im", "in", "aus", "auf",
"ist", "sein", "war", "wird",
"ihr", "ihre", "ihres",
"als", "für", "von", "mit",
"dich", "dir", "mich", "mir",
"mein", "sein", "kein",
"durch", "wegen", "wird"
};
/** File containing default German stopwords. */
public final static 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 {
/** @deprecated in 3.1, remove in Lucene 5.0 (index bw compat) */
@Deprecated
private static final CharArraySet DEFAULT_SET_30 = CharArraySet.unmodifiableSet(new CharArraySet(
Version.LUCENE_CURRENT, Arrays.asList(GERMAN_STOP_WORDS), false));
private static final CharArraySet DEFAULT_SET;
static {
try {
DEFAULT_SET = WordlistLoader.getSnowballWordSet(IOUtils.getDecodingReader(SnowballFilter.class,
DEFAULT_STOPWORD_FILE, IOUtils.CHARSET_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");
}
}
}
/**
* 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(Version matchVersion) {
this(matchVersion,
matchVersion.onOrAfter(Version.LUCENE_31) ? DefaultSetHolder.DEFAULT_SET
: DefaultSetHolder.DEFAULT_SET_30);
}
/**
* Builds an analyzer with the given stop words
*
* @param matchVersion
* lucene compatibility version
* @param stopwords
* a stopword set
*/
public GermanAnalyzer(Version matchVersion, CharArraySet stopwords) {
this(matchVersion, stopwords, CharArraySet.EMPTY_SET);
}
/**
* Builds an analyzer with the given stop words
*
* @param matchVersion
* lucene compatibility version
* @param stopwords
* a stopword set
* @param stemExclusionSet
* a stemming exclusion set
*/
public GermanAnalyzer(Version matchVersion, CharArraySet stopwords, CharArraySet stemExclusionSet) {
super(matchVersion, stopwords);
exclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(matchVersion, 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 StandardFilter}, {@link LowerCaseFilter}, {@link StopFilter}
* , {@link KeywordMarkerFilter} if a stem exclusion set is
* provided, {@link GermanNormalizationFilter} and {@link GermanLightStemFilter}
*/
@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);
result = new KeywordMarkerFilter(result, exclusionSet);
if (matchVersion.onOrAfter(Version.LUCENE_36)) {
result = new GermanNormalizationFilter(result);
result = new GermanLightStemFilter(result);
} else if (matchVersion.onOrAfter(Version.LUCENE_31)) {
result = new SnowballFilter(result, new German2Stemmer());
} else {
result = new GermanStemFilter(result);
}
return new TokenStreamComponents(source, result);
}
}