| /* |
| * 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. |
| */ |
| package org.apache.lucene.analysis.snowball; |
| |
| import java.io.IOException; |
| import org.apache.lucene.analysis.LowerCaseFilter; |
| 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; |
| import org.apache.lucene.analysis.tr.TurkishLowerCaseFilter; // javadoc @link |
| import org.tartarus.snowball.SnowballStemmer; |
| |
| /** |
| * A filter that stems words using a Snowball-generated stemmer. |
| * |
| * <p>Available stemmers are listed in {@link org.tartarus.snowball.ext}. |
| * |
| * <p><b>NOTE</b>: SnowballFilter expects lowercased text. |
| * |
| * <ul> |
| * <li>For the Turkish language, see {@link TurkishLowerCaseFilter}. |
| * <li>For other languages, see {@link LowerCaseFilter}. |
| * </ul> |
| * |
| * <p>Note: This filter is aware of the {@link KeywordAttribute}. To prevent certain terms from |
| * being passed to the stemmer {@link KeywordAttribute#isKeyword()} should be set to <code>true |
| * </code> in a previous {@link TokenStream}. |
| * |
| * <p>Note: For including the original term as well as the stemmed version, see {@link |
| * org.apache.lucene.analysis.miscellaneous.KeywordRepeatFilterFactory} |
| */ |
| public final class SnowballFilter extends TokenFilter { |
| |
| private final SnowballStemmer stemmer; |
| |
| private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class); |
| private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class); |
| |
| public SnowballFilter(TokenStream input, SnowballStemmer stemmer) { |
| super(input); |
| this.stemmer = stemmer; |
| } |
| |
| /** |
| * Construct the named stemming filter. |
| * |
| * <p>Available stemmers are listed in {@link org.tartarus.snowball.ext}. The name of a stemmer is |
| * the part of the class name before "Stemmer", e.g., the stemmer in {@link |
| * org.tartarus.snowball.ext.EnglishStemmer} is named "English". |
| * |
| * @param in the input tokens to stem |
| * @param name the name of a stemmer |
| */ |
| public SnowballFilter(TokenStream in, String name) { |
| super(in); |
| // Class.forName is frowned upon in place of the ResourceLoader but in this case, |
| // the factory will use the other constructor so that the program is already loaded. |
| try { |
| Class<? extends SnowballStemmer> stemClass = |
| Class.forName("org.tartarus.snowball.ext." + name + "Stemmer") |
| .asSubclass(SnowballStemmer.class); |
| stemmer = stemClass.getConstructor().newInstance(); |
| } catch (Exception e) { |
| throw new IllegalArgumentException("Invalid stemmer class specified: " + name, e); |
| } |
| } |
| |
| /** Returns the next input Token, after being stemmed */ |
| @Override |
| public final boolean incrementToken() throws IOException { |
| if (input.incrementToken()) { |
| if (!keywordAttr.isKeyword()) { |
| char termBuffer[] = termAtt.buffer(); |
| final int length = termAtt.length(); |
| stemmer.setCurrent(termBuffer, length); |
| stemmer.stem(); |
| final char finalTerm[] = stemmer.getCurrentBuffer(); |
| final int newLength = stemmer.getCurrentBufferLength(); |
| if (finalTerm != termBuffer) termAtt.copyBuffer(finalTerm, 0, newLength); |
| else termAtt.setLength(newLength); |
| } |
| return true; |
| } else { |
| return false; |
| } |
| } |
| } |