Lucene example source code file (RussianStemFilter.java)

This example Lucene source code file (RussianStemFilter.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

chartermattribute, deprecated, io, ioexception, ioexception, keywordattribute, override, russianstemfilter, russianstemfilter, russianstemmer, russianstemmer, string, string, tokenfilter

The Lucene RussianStemFilter.java source code

package org.apache.lucene.analysis.ru;

/**
 * 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 org.apache.lucene.analysis.KeywordMarkerFilter;// for javadoc
import org.apache.lucene.analysis.LowerCaseFilter; // 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;
import org.apache.lucene.analysis.ru.RussianStemmer;//javadoc @link
import org.apache.lucene.analysis.snowball.SnowballFilter; // javadoc @link

import java.io.IOException;

/**
 * A {@link TokenFilter} that stems Russian words. 
 * <p>
 * The implementation was inspired by GermanStemFilter.
 * The input should be filtered by {@link LowerCaseFilter} before passing it to RussianStemFilter ,
 * because RussianStemFilter only works with lowercase characters.
 * </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 Use {@link SnowballFilter} with 
 * {@link org.tartarus.snowball.ext.RussianStemmer} instead, which has the
 * same functionality. This filter will be removed in Lucene 4.0
 */
@Deprecated
public final class RussianStemFilter extends TokenFilter
{
    /**
     * The actual token in the input stream.
     */
    private RussianStemmer stemmer = new RussianStemmer();

    private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
    private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);

    public RussianStemFilter(TokenStream in)
    {
        super(in);
    }
    /**
     * Returns the next token in the stream, or null at EOS
     */
    @Override
    public final boolean incrementToken() throws IOException
    {
      if (input.incrementToken()) {
        if(!keywordAttr.isKeyword()) {
          final String term = termAtt.toString();
          final String s = stemmer.stem(term);
          if (s != null && !s.equals(term))
            termAtt.setEmpty().append(s);
        }
        return true;
      } else {
        return false;
      }
    }


    /**
     * Set a alternative/custom {@link RussianStemmer} for this filter.
     */
    public void setStemmer(RussianStemmer stemmer)
    {
        if (stemmer != null)
        {
            this.stemmer = stemmer;
        }
    }
}