package org.apache.lucene.analysis.nl;
/**
* 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 org.apache.lucene.analysis.Token;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;
import java.util.Map;
/**
* A filter that stems Dutch words. It supports a table of words that should
* not be stemmed at all. The stemmer used can be changed at runtime after the
* filter object is created (as long as it is a DutchStemmer).
*
* @author Edwin de Jonge
*/
public final class DutchStemFilter extends TokenFilter {
/**
* The actual token in the input stream.
*/
private Token token = null;
private DutchStemmer stemmer = null;
private Set exclusions = null;
public DutchStemFilter(TokenStream _in) {
super(_in);
stemmer = new DutchStemmer();
}
/**
* Builds a DutchStemFilter that uses an exclusiontable.
*/
public DutchStemFilter(TokenStream _in, Set exclusiontable) {
this(_in);
exclusions = exclusiontable;
}
/**
* @param stemdictionary Dictionary of word stem pairs, that overrule the algorithm
*/
public DutchStemFilter(TokenStream _in, Set exclusiontable, Map stemdictionary) {
this(_in, exclusiontable);
stemmer.setStemDictionary(stemdictionary);
}
/**
* @return Returns the next token in the stream, or null at EOS
*/
public Token next() throws IOException {
if ((token = input.next()) == null) {
return null;
}
// Check the exclusiontable
else if (exclusions != null && exclusions.contains(token.termText())) {
return token;
} else {
String s = stemmer.stem(token.termText());
// If not stemmed, dont waste the time creating a new token
if (!s.equals(token.termText())) {
return new Token(s, token.startOffset(),
token.endOffset(), token.type());
}
return token;
}
}
/**
* Set a alternative/custom DutchStemmer for this filter.
*/
public void setStemmer(DutchStemmer stemmer) {
if (stemmer != null) {
this.stemmer = stemmer;
}
}
/**
* Set an alternative exclusion list for this filter.
*/
public void setExclusionTable(HashSet exclusiontable) {
exclusions = exclusiontable;
}
/**
* Set dictionary for stemming, this dictionary overrules the algorithm,
* so you can correct for a particular unwanted word-stem pair.
*/
public void setStemDictionary(HashMap dict) {
if (stemmer != null)
stemmer.setStemDictionary(dict);
}
} |