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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.en;
import java.io.Reader;
import java.util.Arrays;
import java.util.List;
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.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
/**
* {@link Analyzer} for English.
*
* @since 3.1
*/
public final class EnglishAnalyzer extends StopwordAnalyzerBase {
/** An unmodifiable set containing some common English words that are not usually useful
for searching.*/
public static final CharArraySet ENGLISH_STOP_WORDS_SET;
static {
final List stopWords = Arrays.asList(
"a", "an", "and", "are", "as", "at", "be", "but", "by",
"for", "if", "in", "into", "is", "it",
"no", "not", "of", "on", "or", "such",
"that", "the", "their", "then", "there", "these",
"they", "this", "to", "was", "will", "with"
);
final CharArraySet stopSet = new CharArraySet(stopWords, false);
ENGLISH_STOP_WORDS_SET = CharArraySet.unmodifiableSet(stopSet);
}
private final CharArraySet stemExclusionSet;
/**
* Returns an unmodifiable instance of the default stop words set.
* @return default stop words set.
*/
public static CharArraySet getDefaultStopSet(){
return ENGLISH_STOP_WORDS_SET;
}
/**
* Builds an analyzer with the default stop words: {@link #getDefaultStopSet}.
*/
public EnglishAnalyzer() {
this(ENGLISH_STOP_WORDS_SET);
}
/**
* Builds an analyzer with the given stop words.
*
* @param stopwords a stopword set
*/
public EnglishAnalyzer(CharArraySet stopwords) {
this(stopwords, CharArraySet.EMPTY_SET);
}
/**
* Builds an analyzer with the given stop words. If a non-empty stem exclusion set is
* provided this analyzer will add a {@link SetKeywordMarkerFilter} before
* stemming.
*
* @param stopwords a stopword set
* @param stemExclusionSet a set of terms not to be stemmed
*/
public EnglishAnalyzer(CharArraySet stopwords, CharArraySet stemExclusionSet) {
super(stopwords);
this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(stemExclusionSet));
}
/**
* Creates a
* {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents}
* which tokenizes all the text in the provided {@link Reader}.
*
* @return A
* {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents}
* built from an {@link StandardTokenizer} filtered with
* {@link EnglishPossessiveFilter},
* {@link LowerCaseFilter}, {@link StopFilter}
* , {@link SetKeywordMarkerFilter} if a stem exclusion set is
* provided and {@link PorterStemFilter}.
*/
@Override
protected TokenStreamComponents createComponents(String fieldName) {
final Tokenizer source = new StandardTokenizer();
TokenStream result = new EnglishPossessiveFilter(source);
result = new LowerCaseFilter(result);
result = new StopFilter(result, stopwords);
if(!stemExclusionSet.isEmpty())
result = new SetKeywordMarkerFilter(result, stemExclusionSet);
result = new PorterStemFilter(result);
return new TokenStreamComponents(source, result);
}
@Override
protected TokenStream normalize(String fieldName, TokenStream in) {
return new LowerCaseFilter(in);
}
}
