Lucene example source code file (GermanAnalyzer.java)

This example Lucene source code file (GermanAnalyzer.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_set, default_stopword_file, deprecated, deprecated, german_stop_words, germananalyzer, germananalyzer, io, ioexception, ioexception, reader, set, set, string, tokenstreamcomponents, util

The Lucene GermanAnalyzer.java source code

package org.apache.lucene.analysis.de;
// This file is encoded in UTF-8

/**
 * 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.File;
import java.io.IOException;
import java.io.Reader;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.KeywordMarkerFilter;
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.snowball.SnowballFilter;
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.util.Version;
import org.tartarus.snowball.ext.German2Stemmer;

/**
 * {@link Analyzer} for German language. 
 * <p>
 * Supports an external list of stopwords (words that
 * will not be indexed at all) and an external list of exclusions (word that will
 * not be stemmed, but indexed).
 * 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 GermanAnalyzer:
 * <ul>
 *   <li> As of 3.1, Snowball stemming is done with SnowballFilter, 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 GermanAnalyzer extends StopwordAnalyzerBase {
  
  /**
   * List of typical german stopwords.
   * @deprecated use {@link #getDefaultStopSet()} instead
   */
  @Deprecated
  public final static String[] GERMAN_STOP_WORDS = {
    "einer", "eine", "eines", "einem", "einen",
    "der", "die", "das", "dass", "daß",
    "du", "er", "sie", "es",
    "was", "wer", "wie", "wir",
    "und", "oder", "ohne", "mit",
    "am", "im", "in", "aus", "auf",
    "ist", "sein", "war", "wird",
    "ihr", "ihre", "ihres",
    "als", "für", "von", "mit",
    "dich", "dir", "mich", "mir",
    "mein", "sein", "kein",
    "durch", "wegen", "wird"
  };
  
  /** File containing default German stopwords. */
  public final static String DEFAULT_STOPWORD_FILE = "german_stop.txt";
  
  /**
   * Returns a set of default German-stopwords 
   * @return a set of default German-stopwords 
   */
  public static final Set<?> getDefaultStopSet(){
    return DefaultSetHolder.DEFAULT_SET;
  }
  
  private static class DefaultSetHolder {
    /** @deprecated remove in Lucene 5.0 */
    @Deprecated
    private static final Set<?> DEFAULT_SET_30 = CharArraySet.unmodifiableSet(new CharArraySet(
        Version.LUCENE_CURRENT, Arrays.asList(GERMAN_STOP_WORDS), false));
    private static final Set<?> DEFAULT_SET;
    static {
      try {
        DEFAULT_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 {@link StopFilter}.
   */
 
  /**
   * Contains words that should be indexed but not stemmed.
   */
  // TODO make this final in 3.1
  private Set<?> exclusionSet;

  /**
   * Builds an analyzer with the default stop words:
   * {@link #getDefaultStopSet()}.
   */
  public GermanAnalyzer(Version matchVersion) {
    this(matchVersion,
        matchVersion.onOrAfter(Version.LUCENE_31) ? DefaultSetHolder.DEFAULT_SET
            : DefaultSetHolder.DEFAULT_SET_30);
  }
  
  /**
   * Builds an analyzer with the given stop words 
   * 
   * @param matchVersion
   *          lucene compatibility version
   * @param stopwords
   *          a stopword set
   */
  public GermanAnalyzer(Version matchVersion, Set<?> stopwords) {
    this(matchVersion, stopwords, CharArraySet.EMPTY_SET);
  }
  
  /**
   * Builds an analyzer with the given stop words
   * 
   * @param matchVersion
   *          lucene compatibility version
   * @param stopwords
   *          a stopword set
   * @param stemExclusionSet
   *          a stemming exclusion set
   */
  public GermanAnalyzer(Version matchVersion, Set<?> stopwords, Set stemExclusionSet) {
    super(matchVersion, stopwords);
    exclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(matchVersion, stemExclusionSet));
  }

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

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

  /**
   * Builds an analyzer with the given stop words.
   * @deprecated use {@link #GermanAnalyzer(Version, Set)}
   */
  @Deprecated
  public GermanAnalyzer(Version matchVersion, File stopwords) throws IOException {
    this(matchVersion, WordlistLoader.getWordSet(stopwords));
  }

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

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

  /**
   * Builds an exclusionlist from the words contained in the given file.
   * @deprecated use {@link #GermanAnalyzer(Version, Set, Set)} instead
   */
  @Deprecated
  public void setStemExclusionTable(File exclusionlist) throws IOException {
    exclusionSet = WordlistLoader.getWordSet(exclusionlist);
    setPreviousTokenStream(null); // force a new stemmer to be created
  }

  /**
   * Creates
   * {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
   * used to tokenize all the text in the provided {@link Reader}.
   * 
   * @return {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
   *         built from a {@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);
    result = new KeywordMarkerFilter(result, exclusionSet);
    if (matchVersion.onOrAfter(Version.LUCENE_31))
      result = new SnowballFilter(result, new German2Stemmer());
    else
      result = new GermanStemFilter(result);
    return new TokenStreamComponents(source, result);
  }
}