Lucene example source code file (StempelFilter.java)

This example Lucene source code file (StempelFilter.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, default_min_length, default_min_length, io, ioexception, keywordattribute, override, stempelfilter, stempelfilter, stempelstemmer, stempelstemmer, stringbuilder, stringbuilder, tokenfilter

The Lucene StempelFilter.java source code

/**
 * Copyright 2004 The Apache Software Foundation
 * 
 * Licensed 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.
 */

package org.apache.lucene.analysis.stempel;

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;

/**
 * Transforms the token stream as per the stemming algorithm.
 * <p>
 * Note: the input to the stemming filter must already be in lower case, so you
 * will need to use LowerCaseFilter or LowerCaseTokenizer farther down the
 * Tokenizer chain in order for this to work properly!
 */
public final class StempelFilter extends TokenFilter {
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final KeywordAttribute keywordAtt = addAttribute(KeywordAttribute.class);
  private final StempelStemmer stemmer;
  private final int minLength;
  
  /**
   * Minimum length of input words to be processed. Shorter words are returned
   * unchanged.
   */
  public static final int DEFAULT_MIN_LENGTH = 3;
  
  /**
   * Create filter using the supplied stemming table.
   * 
   * @param in input token stream
   * @param stemmer stemmer
   */
  public StempelFilter(TokenStream in, StempelStemmer stemmer) {
    this(in, stemmer, DEFAULT_MIN_LENGTH);
  }
  
  /**
   * Create filter using the supplied stemming table.
   * 
   * @param in input token stream
   * @param stemmer stemmer
   * @param minLength For performance reasons words shorter than minLength
   * characters are not processed, but simply returned.
   */
  public StempelFilter(TokenStream in, StempelStemmer stemmer, int minLength) {
    super(in);
    this.stemmer = stemmer;
    this.minLength = minLength;
  }
  
  /** Returns the next input Token, after being stemmed */
  @Override
  public boolean incrementToken() throws IOException {
    if (input.incrementToken()) {
      if (!keywordAtt.isKeyword() && termAtt.length() > minLength) {
        StringBuilder sb = stemmer.stem(termAtt);
        if (sb != null) // if we can't stem it, return unchanged
          termAtt.setEmpty().append(sb);
      }
      return true;
    } else {
      return false;
    }
  }
}