Lucene example source code file (DutchAnalyzer.java)

This example Lucene source code file (DutchAnalyzer.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, deprecated, deprecated, dutchanalyzer, dutchanalyzer, io, ioexception, runtimeexception, set, set, stopfilter, string, string, tokenizer, tokenstreamcomponents, util

The Lucene DutchAnalyzer.java source code

package org.apache.lucene.analysis.nl;

/**
 * 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 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.ReusableAnalyzerBase;
import org.apache.lucene.analysis.StopFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.WordlistLoader;
import org.apache.lucene.analysis.miscellaneous.StemmerOverrideFilter;
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.analysis.standard.StandardAnalyzer;  // for javadoc
import org.apache.lucene.util.Version;

import java.io.File;
import java.io.IOException;
import java.io.Reader;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;
import java.util.Map;

/**
 * {@link Analyzer} for Dutch language. 
 * <p>
 * Supports an external list of stopwords (words that
 * will not be indexed at all), an external list of exclusions (word that will
 * not be stemmed, but indexed) and an external list of word-stem pairs that overrule
 * the algorithm (dictionary stemming).
 * A default set of stopwords is used unless an alternative list is specified, but the
 * exclusion list is empty by default.
 * </p>
 *
 * <a name="version"/>
 * <p>You must specify the required {@link Version}
 * compatibility when creating DutchAnalyzer:
 * <ul>
 *   <li> As of 3.1, Snowball stemming is done with SnowballFilter, 
 *        LowerCaseFilter is used prior to StopFilter, and Snowball 
 *        stopwords are used by default.
 *   <li> As of 2.9, StopFilter preserves position
 *        increments
 * </ul>
 * 
 * <p>NOTE: This class uses the same {@link Version}
 * dependent settings as {@link StandardAnalyzer}.</p>
 */
public final class DutchAnalyzer extends ReusableAnalyzerBase {
  /**
   * List of typical Dutch stopwords.
   * @deprecated use {@link #getDefaultStopSet()} instead
   */
  @Deprecated
  public final static String[] DUTCH_STOP_WORDS = getDefaultStopSet().toArray(new String[0]);
  
  /** File containing default Dutch stopwords. */
  public final static String DEFAULT_STOPWORD_FILE = "dutch_stop.txt";

  /**
   * Returns an unmodifiable instance of the default stop-words set.
   * @return an unmodifiable instance of the default stop-words set.
   */
  public static Set<?> getDefaultStopSet(){
    return DefaultSetHolder.DEFAULT_STOP_SET;
  }
  
  private static class DefaultSetHolder {
    static final Set<?> DEFAULT_STOP_SET;

    static {
      try {
        DEFAULT_STOP_SET = WordlistLoader.getSnowballWordSet(SnowballFilter.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");
      }
    }
  }


  /**
   * Contains the stopwords used with the StopFilter.
   */
  private final Set<?> stoptable;

  /**
   * Contains words that should be indexed but not stemmed.
   */
  private Set<?> excltable = Collections.emptySet();

  private Map<String, String> stemdict = new HashMap();
  private final Version matchVersion;

  /**
   * Builds an analyzer with the default stop words ({@link #getDefaultStopSet()}) 
   * and a few default entries for the stem exclusion table.
   * 
   */
  public DutchAnalyzer(Version matchVersion) {
    this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET);
    stemdict.put("fiets", "fiets"); //otherwise fiet
    stemdict.put("bromfiets", "bromfiets"); //otherwise bromfiet
    stemdict.put("ei", "eier");
    stemdict.put("kind", "kinder");
  }
  
  public DutchAnalyzer(Version matchVersion, Set<?> stopwords){
    this(matchVersion, stopwords, CharArraySet.EMPTY_SET);
  }
  
  public DutchAnalyzer(Version matchVersion, Set<?> stopwords, Set stemExclusionTable){
    stoptable = CharArraySet.unmodifiableSet(CharArraySet.copy(matchVersion, stopwords));
    excltable = CharArraySet.unmodifiableSet(CharArraySet.copy(matchVersion, stemExclusionTable));
    this.matchVersion = matchVersion;
  }

  /**
   * Builds an analyzer with the given stop words.
   *
   * @param matchVersion
   * @param stopwords
   * @deprecated use {@link #DutchAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public DutchAnalyzer(Version matchVersion, String... stopwords) {
    this(matchVersion, StopFilter.makeStopSet(matchVersion, stopwords));
  }

  /**
   * Builds an analyzer with the given stop words.
   *
   * @param stopwords
   * @deprecated use {@link #DutchAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public DutchAnalyzer(Version matchVersion, HashSet<?> stopwords) {
    this(matchVersion, (Set<?>)stopwords);
  }

  /**
   * Builds an analyzer with the given stop words.
   *
   * @param stopwords
   * @deprecated use {@link #DutchAnalyzer(Version, Set)} instead
   */
  @Deprecated
  public DutchAnalyzer(Version matchVersion, File stopwords) {
    // this is completely broken!
    try {
      stoptable = org.apache.lucene.analysis.WordlistLoader.getWordSet(stopwords);
    } catch (IOException e) {
      // TODO: throw IOException
      throw new RuntimeException(e);
    }
    this.matchVersion = matchVersion;
  }

  /**
   * Builds an exclusionlist from an array of Strings.
   *
   * @param exclusionlist
   * @deprecated use {@link #DutchAnalyzer(Version, Set, Set)} instead
   */
  @Deprecated
  public void setStemExclusionTable(String... exclusionlist) {
    excltable = StopFilter.makeStopSet(matchVersion, exclusionlist);
    setPreviousTokenStream(null); // force a new stemmer to be created
  }

  /**
   * Builds an exclusionlist from a Hashtable.
   * @deprecated use {@link #DutchAnalyzer(Version, Set, Set)} instead
   */
  @Deprecated
  public void setStemExclusionTable(HashSet<?> exclusionlist) {
    excltable = exclusionlist;
    setPreviousTokenStream(null); // force a new stemmer to be created
  }

  /**
   * Builds an exclusionlist from the words contained in the given file.
   * @deprecated use {@link #DutchAnalyzer(Version, Set, Set)} instead
   */
  @Deprecated
  public void setStemExclusionTable(File exclusionlist) {
    try {
      excltable = org.apache.lucene.analysis.WordlistLoader.getWordSet(exclusionlist);
      setPreviousTokenStream(null); // force a new stemmer to be created
    } catch (IOException e) {
      // TODO: throw IOException
      throw new RuntimeException(e);
    }
  }

  /**
   * Reads a stemdictionary file , that overrules the stemming algorithm
   * This is a textfile that contains per line
   * <tt>word\tstem, i.e: two tab seperated words
   */
  public void setStemDictionary(File stemdictFile) {
    try {
      stemdict = WordlistLoader.getStemDict(stemdictFile);
      setPreviousTokenStream(null); // force a new stemmer to be created
    } catch (IOException e) {
      // TODO: throw IOException
      throw new RuntimeException(e);
    }
  }


  /**
   * Returns a (possibly reused) {@link TokenStream} which tokenizes all the 
   * text in the provided {@link Reader}.
   *
   * @return A {@link TokenStream} built from a {@link StandardTokenizer}
   *   filtered with {@link StandardFilter}, {@link LowerCaseFilter}, 
   *   {@link StopFilter}, {@link KeywordMarkerFilter} if a stem exclusion set is provided,
   *   {@link StemmerOverrideFilter}, and {@link SnowballFilter}
   */
  @Override
  protected TokenStreamComponents createComponents(String fieldName,
      Reader aReader) {
    if (matchVersion.onOrAfter(Version.LUCENE_31)) {
      final Tokenizer source = new StandardTokenizer(matchVersion, aReader);
      TokenStream result = new StandardFilter(matchVersion, source);
      result = new LowerCaseFilter(matchVersion, result);
      result = new StopFilter(matchVersion, result, stoptable);
      if (!excltable.isEmpty())
        result = new KeywordMarkerFilter(result, excltable);
      if (!stemdict.isEmpty())
        result = new StemmerOverrideFilter(matchVersion, result, stemdict);
      result = new SnowballFilter(result, new org.tartarus.snowball.ext.DutchStemmer());
      return new TokenStreamComponents(source, result);
    } else {
      final Tokenizer source = new StandardTokenizer(matchVersion, aReader);
      TokenStream result = new StandardFilter(matchVersion, source);
      result = new StopFilter(matchVersion, result, stoptable);
      if (!excltable.isEmpty())
        result = new KeywordMarkerFilter(result, excltable);
      result = new DutchStemFilter(result, stemdict);
      return new TokenStreamComponents(source, result);
    }
  }
}