| /* |
| * 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.en; |
| |
| |
| import java.io.IOException; |
| |
| 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; |
| |
| /** Transforms the token stream as per the Porter stemming algorithm. |
| 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! |
| <P> |
| To use this filter with other analyzers, you'll want to write an |
| Analyzer class that sets up the TokenStream chain as you want it. |
| To use this with LowerCaseTokenizer, for example, you'd write an |
| analyzer like this: |
| <br> |
| <PRE class="prettyprint"> |
| class MyAnalyzer extends Analyzer { |
| {@literal @Override} |
| protected TokenStreamComponents createComponents(String fieldName) { |
| Tokenizer source = new LowerCaseTokenizer(version, reader); |
| return new TokenStreamComponents(source, new PorterStemFilter(source)); |
| } |
| } |
| </PRE> |
| <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}. |
| |
| Note: For including the original term as well as the stemmed version, see |
| {@link org.apache.lucene.analysis.miscellaneous.KeywordRepeatFilterFactory} |
| </p> |
| */ |
| public final class PorterStemFilter extends TokenFilter { |
| private final PorterStemmer stemmer = new PorterStemmer(); |
| private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class); |
| private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class); |
| |
| public PorterStemFilter(TokenStream in) { |
| super(in); |
| } |
| |
| @Override |
| public final boolean incrementToken() throws IOException { |
| if (!input.incrementToken()) |
| return false; |
| |
| if ((!keywordAttr.isKeyword()) && stemmer.stem(termAtt.buffer(), 0, termAtt.length())) |
| termAtt.copyBuffer(stemmer.getResultBuffer(), 0, stemmer.getResultLength()); |
| return true; |
| } |
| } |