package org.apache.lucene.analysis.snowball;
/**
* 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 org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.TermAttribute;
import org.tartarus.snowball.SnowballProgram;
/**
* A filter that stems words using a Snowball-generated stemmer.
*
* Available stemmers are listed in {@link org.tartarus.snowball.ext}.
*/
public final class SnowballFilter extends TokenFilter {
private SnowballProgram stemmer;
private TermAttribute termAtt;
public SnowballFilter(TokenStream input, SnowballProgram stemmer) {
super(input);
this.stemmer = stemmer;
termAtt = addAttribute(TermAttribute.class);
}
/**
* Construct the named stemming filter.
*
* 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);
try {
Class<?> stemClass = Class.forName("org.tartarus.snowball.ext." + name + "Stemmer");
stemmer = (SnowballProgram) stemClass.newInstance();
} catch (Exception e) {
throw new RuntimeException(e.toString());
}
termAtt = addAttribute(TermAttribute.class);
}
/** Returns the next input Token, after being stemmed */
@Override
public final boolean incrementToken() throws IOException {
if (input.incrementToken()) {
String originalTerm = termAtt.term();
stemmer.setCurrent(originalTerm);
stemmer.stem();
String finalTerm = stemmer.getCurrent();
// Don't bother updating, if it is unchanged.
if (!originalTerm.equals(finalTerm))
termAtt.setTermBuffer(finalTerm);
return true;
} else {
return false;
}
}
}