core/org.eclipse.smila.solr/lib/source/org/apache/lucene/analysis/nl/DutchStemFilter.java

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.Map;

import org.apache.lucene.analysis.miscellaneous.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 (3.1) 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 final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);

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

  /**
   * @param stemdictionary Dictionary of word stem pairs, that overrule the algorithm
   */
  public DutchStemFilter(TokenStream _in,  Map<?,?> stemdictionary) {
    this(_in);
    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()) {
        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 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);
  }
}