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Lucene example source code file (DutchStemFilter.java)

This example Lucene source code file (DutchStemFilter.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

deprecated, deprecated, dutchstemfilter, dutchstemfilter, dutchstemmer, io, ioexception, keywordattribute, map, override, set, set, string, string, tokenfilter, util

The Lucene DutchStemFilter.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 java.io.IOException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import org.apache.lucene.analysis.KeywordMarkerFilter;// for javadoc
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.snowball.SnowballFilter;
import org.apache.lucene.analysis.tokenattributes.KeywordAttribute;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;

/**
 * A {@link TokenFilter} that stems Dutch words. 
 * <p>
 * It supports a table of words that should
 * not be stemmed at all. The stemmer used can be changed at runtime after the
 * filter object is created (as long as it is a {@link DutchStemmer}).
 * </p>
 * <p>
 * To prevent terms from being stemmed use an instance of
 * {@link KeywordMarkerFilter} or a custom {@link TokenFilter} that sets
 * the {@link KeywordAttribute} before this {@link TokenStream}.
 * </p>
 * @see KeywordMarkerFilter
 * @deprecated Use {@link SnowballFilter} with 
 * {@link org.tartarus.snowball.ext.DutchStemmer} instead, which has the
 * same functionality. This filter will be removed in Lucene 5.0
 */
@Deprecated
public final class DutchStemFilter extends TokenFilter {
  /**
   * The actual token in the input stream.
   */
  private DutchStemmer stemmer = new DutchStemmer();
  private Set<?> exclusions = null;
  
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);

  public DutchStemFilter(TokenStream _in) {
    super(_in);
  }

  /**
   * Builds a DutchStemFilter that uses an exclusion table.
   * @deprecated use {@link KeywordAttribute} with {@link KeywordMarkerFilter} instead.
   */
  @Deprecated
  public DutchStemFilter(TokenStream _in, Set<?> exclusiontable) {
    this(_in);
    exclusions = exclusiontable;
  }
  
  /**
   * @param stemdictionary Dictionary of word stem pairs, that overrule the algorithm
   */
  public DutchStemFilter(TokenStream _in,  Map<?,?> stemdictionary) {
    this(_in);
    stemmer.setStemDictionary(stemdictionary);
  }

  /**
   * @param stemdictionary Dictionary of word stem pairs, that overrule the algorithm
   * @deprecated use {@link KeywordAttribute} with {@link KeywordMarkerFilter} instead.
   */
  @Deprecated
  public DutchStemFilter(TokenStream _in, Set<?> exclusiontable, Map stemdictionary) {
    this(_in, exclusiontable);
    stemmer.setStemDictionary(stemdictionary);
  }

  /**
   * Returns the next token in the stream, or null at EOS
   */
  @Override
  public boolean incrementToken() throws IOException {
    if (input.incrementToken()) {
      final String term = termAtt.toString();

      // Check the exclusion table.
      if (!keywordAttr.isKeyword() && (exclusions == null || !exclusions.contains(term))) {
        final String s = stemmer.stem(term);
        // If not stemmed, don't waste the time adjusting the token.
        if ((s != null) && !s.equals(term))
          termAtt.setEmpty().append(s);
      }
      return true;
    } else {
      return false;
    }
  }

  /**
   * Set a alternative/custom {@link DutchStemmer} for this filter.
   */
  public void setStemmer(DutchStemmer stemmer) {
    if (stemmer != null) {
      this.stemmer = stemmer;
    }
  }

  /**
   * Set an alternative exclusion list for this filter.
   * @deprecated use {@link KeywordAttribute} with {@link KeywordMarkerFilter} instead.
   */
  @Deprecated
  public void setExclusionTable(HashSet<?> exclusiontable) {
    exclusions = exclusiontable;
  }

  /**
   * Set dictionary for stemming, this dictionary overrules the algorithm,
   * so you can correct for a particular unwanted word-stem pair.
   */
  public void setStemDictionary(HashMap<?,?> dict) {
    if (stemmer != null)
      stemmer.setStemDictionary(dict);
  }
}

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