content: package org.apache.lucene.analysis.snowball;
  
  /**
   * 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 org.apache.lucene.analysis.TokenFilter;
  import org.apache.lucene.analysis.TokenStream;
  import org.apache.lucene.analysis.tokenattributes.KeywordAttribute;
  import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
  import org.apache.lucene.analysis.tr.TurkishLowerCaseFilter; // javadoc @link
  import org.apache.lucene.analysis.LowerCaseFilter; // javadoc @link
  import org.tartarus.snowball.SnowballProgram;
  
  /**
   * A filter that stems words using a Snowball-generated stemmer.
   *
   * Available stemmers are listed in {@link org.tartarus.snowball.ext}.
   * <p><b>NOTE</b>: SnowballFilter expects lowercased text.
   * <ul>
   *  <li>For the Turkish language, see {@link TurkishLowerCaseFilter}.
   *  <li>For other languages, see {@link LowerCaseFilter}.
   * </ul>
   * </p>
   */
  public final class SnowballFilter extends TokenFilter {
  
    private final SnowballProgram stemmer;
  
    private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
    private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);
    
    public SnowballFilter(TokenStream input, SnowballProgram stemmer) {
      super(input);
      this.stemmer = stemmer;
    }
  
    /**
     * Construct the named stemming filter.
     *
     * Available stemmers are listed in {@link org.tartarus.snowball.ext}.
     * The name of a stemmer is the part of the class name before "Stemmer",
     * e.g., the stemmer in {@link org.tartarus.snowball.ext.EnglishStemmer} is named "English".
     *
     * @param in the input tokens to stem
     * @param name the name of a stemmer
     */
    public SnowballFilter(TokenStream in, String name) {
      super(in);
      try {      
        Class<?> stemClass = Class.forName("org.tartarus.snowball.ext." + name + "Stemmer");
        stemmer = (SnowballProgram) stemClass.newInstance();
      } catch (Exception e) {
        throw new RuntimeException(e.toString());
      }
    }
  
    /** Returns the next input Token, after being stemmed */
    @Override
    public final boolean incrementToken() throws IOException {
      if (input.incrementToken()) {
        if (!keywordAttr.isKeyword()) {
          char termBuffer[] = termAtt.buffer();
          final int length = termAtt.length();
          stemmer.setCurrent(termBuffer, length);
          stemmer.stem();
          final char finalTerm[] = stemmer.getCurrentBuffer();
          final int newLength = stemmer.getCurrentBufferLength();
          if (finalTerm != termBuffer)
            termAtt.copyBuffer(finalTerm, 0, newLength);
          else
            termAtt.setLength(newLength);
        }
        return true;
      } else {
        return false;
      }
    }
  }
  