content: package org.apache.lucene.analysis.de;
  
  /**
   * 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.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.tokenattributes.KeywordAttribute;
  import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
  
  /**
   * A {@link TokenFilter} that stems German 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 GermanStemmer}).
   * </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
   */
  public final class GermanStemFilter extends TokenFilter
  {
      /**
       * The actual token in the input stream.
       */
      private GermanStemmer stemmer = new GermanStemmer();
      private Set<?> exclusionSet = null;
  
      private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
      private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);
  
      /**
       * Creates a {@link GermanStemFilter} instance
       * @param in the source {@link TokenStream} 
       */
      public GermanStemFilter( TokenStream in )
      {
        super(in);
      }
  
      /**
       * Builds a GermanStemFilter that uses an exclusion table.
       * @deprecated use {@link KeywordAttribute} with {@link KeywordMarkerFilter} instead.
       */
      @Deprecated
      public GermanStemFilter( TokenStream in, Set<?> exclusionSet )
      {
        this( in );
        this.exclusionSet = exclusionSet;
      }
  
      /**
       * @return  Returns true for next token in the stream, or false at EOS
       */
      @Override
      public boolean incrementToken() throws IOException {
        if (input.incrementToken()) {
          String term = termAtt.toString();
          // Check the exclusion table.
          if (!keywordAttr.isKeyword() && (exclusionSet == null || !exclusionSet.contains(term))) {
            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 GermanStemmer} for this filter.
       */
      public void setStemmer( GermanStemmer 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 setExclusionSet( Set<?> exclusionSet )
      {
        this.exclusionSet = exclusionSet;
      }
  }
  