package org.apache.lucene.analysis.de;
/**
* 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 java.util.Set;
import org.apache.lucene.analysis.miscellaneous.KeywordMarkerFilter; // for javadoc
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;
/**
* A {@link TokenFilter} that stems German words.
* <p>
* 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 {@link GermanStemmer}).
* </p>
* <p>
* To prevent terms from being stemmed use an instance of
* {@link KeywordMarkerFilter} or a custom {@link TokenFilter} that sets
* the {@link KeywordAttribute} before this {@link TokenStream}.
* </p>
* @see KeywordMarkerFilter
*/
public final class GermanStemFilter extends TokenFilter
{
/**
* The actual token in the input stream.
*/
private GermanStemmer stemmer = new GermanStemmer();
private Set<?> exclusionSet = null;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class);
/**
* Creates a {@link GermanStemFilter} instance
* @param in the source {@link TokenStream}
*/
public GermanStemFilter( TokenStream in )
{
super(in);
}
/**
* Builds a GermanStemFilter that uses an exclusion table.
* @deprecated use {@link KeywordAttribute} with {@link KeywordMarkerFilter} instead.
*/
@Deprecated
public GermanStemFilter( TokenStream in, Set<?> exclusionSet )
{
this( in );
this.exclusionSet = exclusionSet;
}
/**
* @return Returns true for next token in the stream, or false at EOS
*/
@Override
public boolean incrementToken() throws IOException {
if (input.incrementToken()) {
String term = termAtt.toString();
// Check the exclusion table.
if (!keywordAttr.isKeyword() && (exclusionSet == null || !exclusionSet.contains(term))) {
String s = stemmer.stem(term);
// If not stemmed, don't waste the time adjusting the token.
if ((s != null) && !s.equals(term))
termAtt.setEmpty().append(s);
}
return true;
} else {
return false;
}
}
/**
* Set a alternative/custom {@link GermanStemmer} for this filter.
*/
public void setStemmer( GermanStemmer stemmer )
{
if ( stemmer != null ) {
this.stemmer = stemmer;
}
}
/**
* Set an alternative exclusion list for this filter.
* @deprecated use {@link KeywordAttribute} with {@link KeywordMarkerFilter} instead.
*/
@Deprecated
public void setExclusionSet( Set<?> exclusionSet )
{
this.exclusionSet = exclusionSet;
}
}