package org.apache.lucene.analysis.core;
/*
* 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.util.Arrays;
import java.util.List;
import org.apache.lucene.analysis.util.FilteringTokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.util.CharArraySet;
import org.apache.lucene.util.Version;
/**
* Removes stop words from a token stream.
*
* <a name="version"/>
* <p>You must specify the required {@link Version}
* compatibility when creating StopFilter:
* <ul>
* <li> As of 3.1, StopFilter correctly handles Unicode 4.0
* supplementary characters in stopwords and position
* increments are preserved
* </ul>
*/
public final class StopFilter extends FilteringTokenFilter {
private final CharArraySet stopWords;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
/**
* Constructs a filter which removes words from the input TokenStream that are
* named in the Set.
*
* @param matchVersion
* Lucene version to enable correct Unicode 4.0 behavior in the stop
* set if Version > 3.0. See <a href="#version">above</a> for details.
* @param in
* Input stream
* @param stopWords
* A {@link CharArraySet} representing the stopwords.
* @see #makeStopSet(Version, java.lang.String...)
*/
public StopFilter(Version matchVersion, TokenStream in, CharArraySet stopWords) {
super(matchVersion, in);
this.stopWords = stopWords;
}
/**
* Builds a Set from an array of stop words,
* appropriate for passing into the StopFilter constructor.
* This permits this stopWords construction to be cached once when
* an Analyzer is constructed.
*
* @param matchVersion Lucene version to enable correct Unicode 4.0 behavior in the returned set if Version > 3.0
* @param stopWords An array of stopwords
* @see #makeStopSet(Version, java.lang.String[], boolean) passing false to ignoreCase
*/
public static CharArraySet makeStopSet(Version matchVersion, String... stopWords) {
return makeStopSet(matchVersion, stopWords, false);
}
/**
* Builds a Set from an array of stop words,
* appropriate for passing into the StopFilter constructor.
* This permits this stopWords construction to be cached once when
* an Analyzer is constructed.
*
* @param matchVersion Lucene version to enable correct Unicode 4.0 behavior in the returned set if Version > 3.0
* @param stopWords A List of Strings or char[] or any other toString()-able list representing the stopwords
* @return A Set ({@link CharArraySet}) containing the words
* @see #makeStopSet(Version, java.lang.String[], boolean) passing false to ignoreCase
*/
public static CharArraySet makeStopSet(Version matchVersion, List<?> stopWords) {
return makeStopSet(matchVersion, stopWords, false);
}
/**
* Creates a stopword set from the given stopword array.
*
* @param matchVersion Lucene version to enable correct Unicode 4.0 behavior in the returned set if Version > 3.0
* @param stopWords An array of stopwords
* @param ignoreCase If true, all words are lower cased first.
* @return a Set containing the words
*/
public static CharArraySet makeStopSet(Version matchVersion, String[] stopWords, boolean ignoreCase) {
CharArraySet stopSet = new CharArraySet(matchVersion, stopWords.length, ignoreCase);
stopSet.addAll(Arrays.asList(stopWords));
return stopSet;
}
/**
* Creates a stopword set from the given stopword list.
* @param matchVersion Lucene version to enable correct Unicode 4.0 behavior in the returned set if Version > 3.0
* @param stopWords A List of Strings or char[] or any other toString()-able list representing the stopwords
* @param ignoreCase if true, all words are lower cased first
* @return A Set ({@link CharArraySet}) containing the words
*/
public static CharArraySet makeStopSet(Version matchVersion, List<?> stopWords, boolean ignoreCase){
CharArraySet stopSet = new CharArraySet(matchVersion, stopWords.size(), ignoreCase);
stopSet.addAll(stopWords);
return stopSet;
}
/**
* Returns the next input Token whose term() is not a stop word.
*/
@Override
protected boolean accept() {
return !stopWords.contains(termAtt.buffer(), 0, termAtt.length());
}
}