content: package org.apache.lucene.analysis.en;
  
  /**
   * 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.CharTermAttribute;
  import org.apache.lucene.analysis.tokenattributes.KeywordAttribute;
  
  /** A high-performance kstem filter for english.
   * <p/>
   * See <a href="http://ciir.cs.umass.edu/pubfiles/ir-35.pdf">
   * "Viewing Morphology as an Inference Process"</a>
   * (Krovetz, R., Proceedings of the Sixteenth Annual International ACM SIGIR
   * Conference on Research and Development in Information Retrieval, 191-203, 1993).
   * <p/>
   * All terms must already be lowercased for this filter to work correctly.
   */
  
  public final class KStemFilter extends TokenFilter {
    private final KStemmer stemmer = new KStemmer();
    private final CharTermAttribute termAttribute = addAttribute(CharTermAttribute.class);
    private final KeywordAttribute keywordAtt = addAttribute(KeywordAttribute.class);
  
    public KStemFilter(TokenStream in) {
      super(in);
    }
  
    /** Returns the next, stemmed, input Token.
     *  @return The stemed form of a token.
     *  @throws IOException
     */
    @Override
    public boolean incrementToken() throws IOException {
      if (!input.incrementToken())
        return false;
  
      char[] term = termAttribute.buffer();
      int len = termAttribute.length();
      if ((!keywordAtt.isKeyword()) && stemmer.stem(term, len)) {
        termAttribute.setEmpty().append(stemmer.asCharSequence());
      }
  
      return true;
    }
  }
  