Lucene example source code file (PolishAnalyzer.java)

This example Lucene source code file (PolishAnalyzer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

default_stop_set, default_stopword_file, default_table, io, ioexception, ioexception, polishanalyzer, polishanalyzer, runtimeexception, set, set, string, tokenstreamcomponents, trie, unable, util

The Lucene PolishAnalyzer.java source code

package org.apache.lucene.analysis.pl;

/**
 * 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.StopwordAnalyzerBase;
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.stempel.StempelStemmer;
import org.apache.lucene.analysis.stempel.StempelFilter;
import org.apache.lucene.util.Version;
import org.egothor.stemmer.Trie;

/**
 * {@link Analyzer} for Polish.
 */
public final class PolishAnalyzer extends StopwordAnalyzerBase {
  private final Set<?> stemExclusionSet;
  private final Trie stemTable;
  
  /** File containing default Polish stopwords. */
  public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";
  
  /** File containing default Polish stemmer table. */
  public final static String DEFAULT_STEMMER_FILE = "stemmer_20000.tbl";
  
  /**
   * Returns an unmodifiable instance of the default stop words set.
   * @return default stop words set.
   */
  public static Set<?> getDefaultStopSet(){
    return DefaultsHolder.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 DefaultsHolder {
    static final Set<?> DEFAULT_STOP_SET;
    static final Trie DEFAULT_TABLE;
    
    static {
      try {
        DEFAULT_STOP_SET = WordlistLoader.getWordSet(PolishAnalyzer.class, 
            DEFAULT_STOPWORD_FILE);
      } 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", ex);
      }
      
      try {
        DEFAULT_TABLE = StempelStemmer.load(PolishAnalyzer.class.getResourceAsStream(DEFAULT_STEMMER_FILE));
      } catch (IOException ex) {
        // default set should always be present as it is part of the
        // distribution (JAR)
        throw new RuntimeException("Unable to load default stemming tables", ex);
      }
    }
  }

  /**
   * Builds an analyzer with the default stop words: {@link #DEFAULT_STOPWORD_FILE}.
   */
  public PolishAnalyzer(Version matchVersion) {
    this(matchVersion, DefaultsHolder.DEFAULT_STOP_SET);
  }
  
  /**
   * Builds an analyzer with the given stop words.
   * 
   * @param matchVersion lucene compatibility version
   * @param stopwords a stopword set
   */
  public PolishAnalyzer(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 PolishAnalyzer(Version matchVersion, Set<?> stopwords, Set stemExclusionSet) {
    super(matchVersion, stopwords);
    this.stemTable = DefaultsHolder.DEFAULT_TABLE;
    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 StempelFilter}.
   */
  @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 StempelFilter(result, new StempelStemmer(stemTable));
    return new TokenStreamComponents(source, result);
  }
}