package org.apache.lucene.analysis.snowball;
/**
* 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.
*/
import java.io.IOException;
import java.lang.reflect.Method;
import net.sf.snowball.SnowballProgram;
import net.sf.snowball.ext.*;
import org.apache.lucene.analysis.Token;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
/** A filter that stems words using a Snowball-generated stemmer.
*
* Available stemmers are listed in {@link net.sf.snowball.ext}. The name of a
* stemmer is the part of the class name before "Stemmer", e.g., the stemmer in
* {@link EnglishStemmer} is named "English".
*/
public class SnowballFilter extends TokenFilter {
private static final Object [] EMPTY_ARGS = new Object[0];
private SnowballProgram stemmer;
private Method stemMethod;
/** Construct the named stemming filter.
*
* @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("net.sf.snowball.ext." + name + "Stemmer");
stemmer = (SnowballProgram) stemClass.newInstance();
// why doesn't the SnowballProgram class have an (abstract?) stem method?
stemMethod = stemClass.getMethod("stem", new Class[0]);
} catch (Exception e) {
throw new RuntimeException(e.toString());
}
}
/** Returns the next input Token, after being stemmed */
public final Token next() throws IOException {
Token token = input.next();
if (token == null)
return null;
stemmer.setCurrent(token.termText());
try {
stemMethod.invoke(stemmer, EMPTY_ARGS);
} catch (Exception e) {
throw new RuntimeException(e.toString());
}
Token newToken = new Token(stemmer.getCurrent(),
token.startOffset(), token.endOffset(), token.type());
newToken.setPositionIncrement(token.getPositionIncrement());
return newToken;
}
}
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