package org.apache.lucene.analysis.de;
/**
* 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.Set;
/**
* A filter that stems German 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 GermanStemmer).
*
* @author Gerhard Schwarz
* @version $Id: GermanStemFilter.java 387550 2006-03-21 15:36:32Z yonik $
*/
public final class GermanStemFilter extends TokenFilter
{
/**
* The actual token in the input stream.
*/
private Token token = null;
private GermanStemmer stemmer = null;
private Set exclusionSet = null;
public GermanStemFilter( TokenStream in )
{
super(in);
stemmer = new GermanStemmer();
}
/**
* Builds a GermanStemFilter that uses an exclusiontable.
*/
public GermanStemFilter( TokenStream in, Set exclusionSet )
{
this( in );
this.exclusionSet = exclusionSet;
}
/**
* @return Returns the next token in the stream, or null at EOS
*/
public final Token next()
throws IOException
{
if ( ( token = input.next() ) == null ) {
return null;
}
// Check the exclusiontable
else if ( exclusionSet != null && exclusionSet.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 GermanStemmer for this filter.
*/
public void setStemmer( GermanStemmer stemmer )
{
if ( stemmer != null ) {
this.stemmer = stemmer;
}
}
/**
* Set an alternative exclusion list for this filter.
*/
public void setExclusionSet( Set exclusionSet )
{
this.exclusionSet = exclusionSet;
}
}
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