EnglishAnalyzerConfigurable.java Source code

Introduction

Here is the source code for EnglishAnalyzerConfigurable.java

Source

/*
 * 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.Reader;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.core.LowerCaseFilter;
import org.apache.lucene.analysis.core.StopFilter;
import org.apache.lucene.analysis.en.EnglishPossessiveFilter;
import org.apache.lucene.analysis.en.KStemFilter;
import org.apache.lucene.analysis.en.PorterStemFilter;
import org.apache.lucene.analysis.miscellaneous.SetKeywordMarkerFilter;
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.util.Version;

/**
 * {@link Analyzer} for English.
 */
public final class EnglishAnalyzerConfigurable extends StopwordAnalyzerBase {

    public enum StemmerType {
        NONE, PORTER, KSTEM
    };

    private final CharArraySet stemExclusionSet;
    private Boolean doLowerCase = true;
    private Boolean doStopwordRemoval = true;
    private StemmerType stemmer = StemmerType.PORTER;

    /**
     * Returns an unmodifiable instance of the default stop words set.
     * 
     * @return default stop words set.
     */
    public static CharArraySet getDefaultStopSet() {
        return DefaultSetHolder.DEFAULT_STOP_SET;
    }

    /**
     * Atomically loads the DEFAULT_STOP_SET in a lazy fashion once the outer
     * class accesses the static final set the first time.;
     */
    private static class DefaultSetHolder {
        static final CharArraySet DEFAULT_STOP_SET = StandardAnalyzer.STOP_WORDS_SET;
    }

    /**
     * Builds an analyzer with the default stop words: {@link #getDefaultStopSet}.
     * @param matchVersion
     *          lucene compatibility version
     */
    public EnglishAnalyzerConfigurable(Version matchVersion) {
        this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET);
    }

    /**
     * Builds an analyzer with the given stop words.
     * 
     * @param matchVersion
     *          lucene compatibility version
     * @param stopwords
     *          a stopword set
     */
    public EnglishAnalyzerConfigurable(Version matchVersion, CharArraySet stopwords) {
        this(matchVersion, 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 matchVersion
     *          lucene compatibility version
     * @param stopwords
     *          a stopword set
     * @param stemExclusionSet
     *          a set of terms not to be stemmed
     */
    public EnglishAnalyzerConfigurable(Version matchVersion, CharArraySet stopwords,
            CharArraySet stemExclusionSet) {
        super(matchVersion, stopwords);
        this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(matchVersion, stemExclusionSet));
    }

    /**
     * Enable or disable the conversion of text to lower case.
     * @param onOff If true, convert text to lower case, otherwise don't.
     */
    public void setLowercase(Boolean onOff) {
        this.doLowerCase = onOff;
    }

    /**
     * Enable or disable stopword removal.
     * @param onOff If true, remove stopwords, otherwise don't.
     */
    public void setStopwordRemoval(Boolean onOff) {
        this.doStopwordRemoval = onOff;
    }

    /**
     * Control whether and how stemming is done. See StemmerType.
     * @param s the stemmer type
     */
    public void setStemmer(StemmerType s) {
        this.stemmer = s;
    }

    /**
     * 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 StandardFilter}, {@link EnglishPossessiveFilter},
     *         {@link LowerCaseFilter}, {@link StopFilter} ,
     *         {@link SetKeywordMarkerFilter} if a stem exclusion set is provided
     *         and {@link PorterStemFilter}.
     */
    @Override
    protected TokenStreamComponents createComponents(String fieldName, Reader reader) {
        final Tokenizer source = new StandardTokenizer(matchVersion, reader);
        TokenStream result = new StandardFilter(matchVersion, source);
        // prior to this we get the classic behavior, standardfilter does it for us.

        result = new EnglishPossessiveFilter(matchVersion, result);

        if (this.doLowerCase)
            result = new LowerCaseFilter(matchVersion, result);

        if (this.doStopwordRemoval)
            result = new StopFilter(matchVersion, result, stopwords);

        if (!stemExclusionSet.isEmpty())
            result = new SetKeywordMarkerFilter(result, stemExclusionSet);

        if (this.stemmer == StemmerType.PORTER)
            result = new PorterStemFilter(result);
        else if (this.stemmer == StemmerType.KSTEM)
            result = new KStemFilter(result);

        return new TokenStreamComponents(source, result);
    }
}