org.apache.lucene.analysis.en.EnglishAnalyzer.java Source code

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Here is the source code for org.apache.lucene.analysis.en.EnglishAnalyzer.java

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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<String> 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);
    }
}