RomanianAnalyzer.java Source code

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Here is the source code for RomanianAnalyzer.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.
 */

import java.io.IOException;
import java.io.Reader;
import java.util.Set;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.KeywordMarkerFilter;
import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.StopFilter;
import org.apache.lucene.analysis.ASCIIFoldingFilter;
import org.apache.lucene.analysis.StopwordAnalyzerBase;
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.StandardFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.Version;
// import org.tartarus.snowball.ext.RomanianStemmer; // use OldRomanianStemmer

/**
 * {@link Analyzer} for Romanian.
 */
public final class RomanianAnalyzer extends StopwordAnalyzerBase {
    private final Set<?> stemExclusionSet;

    /** File containing default Romanian stopwords. */
    public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";
    /**
     * The comment character in the stopwords file.  
     * All lines prefixed with this will be ignored.
     */
    private static final String STOPWORDS_COMMENT = "#";

    /**
     * Returns an unmodifiable instance of the default stop words set.
     * @return default stop words set.
     */
    public static Set<?> 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 Set<?> DEFAULT_STOP_SET;

        static {
            try {
                DEFAULT_STOP_SET = loadStopwordSet(false, RomanianAnalyzer.class, DEFAULT_STOPWORD_FILE,
                        STOPWORDS_COMMENT);
            } 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");
            }
        }
    }

    /**
     * Builds an analyzer with the default stop words: {@link #DEFAULT_STOPWORD_FILE}.
     */
    public RomanianAnalyzer(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 RomanianAnalyzer(Version matchVersion, Set<?> 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 KeywordMarkerFilter} before
     * stemming.
     * 
     * @param matchVersion lucene compatibility version
     * @param stopwords a stopword set
     * @param stemExclusionSet a set of terms not to be stemmed
     */
    public RomanianAnalyzer(Version matchVersion, Set<?> stopwords, Set<?> stemExclusionSet) {
        super(matchVersion, stopwords);
        this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(matchVersion, stemExclusionSet));
    }

    /**
     * Creates a
     * {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
     * which tokenizes all the text in the provided {@link Reader}.
     * 
     * @return A
     *         {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
     *         built from an {@link StandardTokenizer} filtered with
     *         {@link StandardFilter}, {@link LowerCaseFilter}, {@link StopFilter}
     *         , {@link KeywordMarkerFilter} if a stem exclusion set is
     *         provided and {@link SnowballFilter}.
     */
    @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);
        if (!stemExclusionSet.isEmpty())
            result = new KeywordMarkerFilter(result, stemExclusionSet);
        result = new SnowballFilter(result, new OldRomanianStemmer());

        result = new ASCIIFoldingFilter(result);
        return new TokenStreamComponents(source, result);
    }
}