Lucene example source code file (StemmerOverrideFilter.java)

This example Lucene source code file (StemmerOverrideFilter.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

chararraymap, chararraymap, chartermattribute, io, ioexception, ioexception, keywordattribute, map, override, stemmeroverridefilter, stemmeroverridefilter, string, tokenfilter, tokenstream, tokenstream, util

The Lucene StemmerOverrideFilter.java source code

package org.apache.lucene.analysis.miscellaneous;

/**
 * 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.Map;

import org.apache.lucene.analysis.CharArrayMap;
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.util.Version;

/**
 * Provides the ability to override any {@link KeywordAttribute} aware stemmer
 * with custom dictionary-based stemming.
 */
public final class StemmerOverrideFilter extends TokenFilter {
  private final CharArrayMap<String> dictionary;
  
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final KeywordAttribute keywordAtt = addAttribute(KeywordAttribute.class);
  
  /**
   * Create a new StemmerOverrideFilter, performing dictionary-based stemming
   * with the provided <code>dictionary.
   * <p>
   * Any dictionary-stemmed terms will be marked with {@link KeywordAttribute}
   * so that they will not be stemmed with stemmers down the chain.
   * </p>
   */
  public StemmerOverrideFilter(Version matchVersion, TokenStream input,
      Map<?,String> dictionary) {
    super(input);
    this.dictionary = dictionary instanceof CharArrayMap ? 
        (CharArrayMap<String>) dictionary : CharArrayMap.copy(matchVersion, dictionary);
  }

  @Override
  public boolean incrementToken() throws IOException {
    if (input.incrementToken()) {
      if (!keywordAtt.isKeyword()) { // don't muck with already-keyworded terms
        String stem = dictionary.get(termAtt.buffer(), 0, termAtt.length());
        if (stem != null) {
          termAtt.setEmpty().append(stem);
          keywordAtt.setKeyword(true);
        }
      }
      return true;
    } else {
      return false;
    }
  }
}