org.apache.lucene.analysis.de.GermanAnalyzer Maven / Gradle / Ivy
package org.apache.lucene.analysis.de;
// This file is encoded in UTF-8
/**
* 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.Arrays;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
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.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.analysis.standard.StandardAnalyzer; // for javadoc
import org.apache.lucene.util.Version;
/**
* {@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 Version}
* dependent settings as {@link StandardAnalyzer}.
*/
public class GermanAnalyzer extends Analyzer {
/**
* List of typical german stopwords.
* @deprecated use {@link #getDefaultStopSet()} instead
*/
//TODO make this private in 3.1
public 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"
};
/**
* Returns a set of default German-stopwords
* @return a set of default German-stopwords
*/
public static final Set getDefaultStopSet(){
return DefaultSetHolder.DEFAULT_SET;
}
private static class DefaultSetHolder {
private static final Set DEFAULT_SET = CharArraySet.unmodifiableSet(new CharArraySet(
Arrays.asList(GERMAN_STOP_WORDS), false));
}
/**
* Contains the stopwords used with the {@link StopFilter}.
*/
//TODO make this final in 3.1
private Set stopSet;
/**
* Contains words that should be indexed but not stemmed.
*/
// TODO make this final in 3.1
private Set exclusionSet;
private final Version matchVersion;
/**
* Builds an analyzer with the default stop words:
* {@link #getDefaultStopSet()}.
*/
public GermanAnalyzer(Version matchVersion) {
this(matchVersion, DefaultSetHolder.DEFAULT_SET);
}
/**
* Builds an analyzer with the given stop words
*
* @param matchVersion
* lucene compatibility version
* @param stopwords
* a stopword set
*/
public GermanAnalyzer(Version matchVersion, Set 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, Set stopwords, Set stemExclusionSet) {
stopSet = CharArraySet.unmodifiableSet(CharArraySet.copy(stopwords));
exclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(stemExclusionSet));
setOverridesTokenStreamMethod(GermanAnalyzer.class);
this.matchVersion = matchVersion;
}
/**
* Builds an analyzer with the given stop words.
* @deprecated use {@link #GermanAnalyzer(Version, Set)}
*/
public GermanAnalyzer(Version matchVersion, String... stopwords) {
this(matchVersion, StopFilter.makeStopSet(stopwords));
}
/**
* Builds an analyzer with the given stop words.
* @deprecated use {@link #GermanAnalyzer(Version, Set)}
*/
public GermanAnalyzer(Version matchVersion, Map stopwords) {
this(matchVersion, stopwords.keySet());
}
/**
* Builds an analyzer with the given stop words.
* @deprecated use {@link #GermanAnalyzer(Version, Set)}
*/
public GermanAnalyzer(Version matchVersion, File stopwords) throws IOException {
this(matchVersion, WordlistLoader.getWordSet(stopwords));
}
/**
* Builds an exclusionlist from an array of Strings.
* @deprecated use {@link #GermanAnalyzer(Version, Set, Set)} instead
*/
public void setStemExclusionTable(String[] exclusionlist) {
exclusionSet = StopFilter.makeStopSet(exclusionlist);
setPreviousTokenStream(null); // force a new stemmer to be created
}
/**
* Builds an exclusionlist from a {@link Map}
* @deprecated use {@link #GermanAnalyzer(Version, Set, Set)} instead
*/
public void setStemExclusionTable(Map exclusionlist) {
exclusionSet = new HashSet(exclusionlist.keySet());
setPreviousTokenStream(null); // force a new stemmer to be created
}
/**
* Builds an exclusionlist from the words contained in the given file.
* @deprecated use {@link #GermanAnalyzer(Version, Set, Set)} instead
*/
public void setStemExclusionTable(File exclusionlist) throws IOException {
exclusionSet = WordlistLoader.getWordSet(exclusionlist);
setPreviousTokenStream(null); // force a new stemmer to be created
}
/**
* Creates a {@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}, and
* {@link GermanStemFilter}
*/
@Override
public TokenStream tokenStream(String fieldName, Reader reader) {
TokenStream result = new StandardTokenizer(matchVersion, reader);
result = new StandardFilter(result);
result = new LowerCaseFilter(result);
result = new StopFilter(StopFilter.getEnablePositionIncrementsVersionDefault(matchVersion),
result, stopSet);
result = new GermanStemFilter(result, exclusionSet);
return result;
}
private class SavedStreams {
Tokenizer source;
TokenStream result;
};
/**
* 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}, and
* {@link GermanStemFilter}
*/
@Override
public TokenStream reusableTokenStream(String fieldName, Reader reader) throws IOException {
if (overridesTokenStreamMethod) {
// LUCENE-1678: force fallback to tokenStream() if we
// have been subclassed and that subclass overrides
// tokenStream but not reusableTokenStream
return tokenStream(fieldName, reader);
}
SavedStreams streams = (SavedStreams) getPreviousTokenStream();
if (streams == null) {
streams = new SavedStreams();
streams.source = new StandardTokenizer(matchVersion, reader);
streams.result = new StandardFilter(streams.source);
streams.result = new LowerCaseFilter(streams.result);
streams.result = new StopFilter(StopFilter.getEnablePositionIncrementsVersionDefault(matchVersion),
streams.result, stopSet);
streams.result = new GermanStemFilter(streams.result, exclusionSet);
setPreviousTokenStream(streams);
} else {
streams.source.reset(reader);
}
return streams.result;
}
}
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