package org.apache.lucene.analysis.th;
/**
* Copyright 2006 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.io.Reader;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.core.LowerCaseFilter;
import org.apache.lucene.analysis.core.StopAnalyzer;
import org.apache.lucene.analysis.core.StopFilter;
import org.apache.lucene.analysis.standard.StandardFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.analysis.util.CharArraySet;
import org.apache.lucene.analysis.util.StopwordAnalyzerBase;
import org.apache.lucene.util.Version;
/**
* {@link Analyzer} for Thai language. It uses {@link java.text.BreakIterator} to break words.
* <p>
* <a name="version"/>
* <p>You must specify the required {@link Version}
* compatibility when creating ThaiAnalyzer:
* <ul>
* <li> As of 3.6, a set of Thai stopwords is used by default
* </ul>
*/
public final class ThaiAnalyzer extends StopwordAnalyzerBase {
/** File containing default Thai stopwords. */
public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";
/**
* The comment character in the stopwords file.
* All lines prefixed with this will be ignored.
*/
private static final String STOPWORDS_COMMENT = "#";
/**
* Returns an unmodifiable instance of the default stop words set.
* @return default stop words set.
*/
public static CharArraySet getDefaultStopSet(){
return DefaultSetHolder.DEFAULT_STOP_SET;
}
/**
* Atomically loads the DEFAULT_STOP_SET in a lazy fashion once the outer class
* accesses the static final set the first time.;
*/
private static class DefaultSetHolder {
static final CharArraySet DEFAULT_STOP_SET;
static {
try {
DEFAULT_STOP_SET = loadStopwordSet(false, ThaiAnalyzer.class,
DEFAULT_STOPWORD_FILE, STOPWORDS_COMMENT);
} catch (IOException ex) {
// default set should always be present as it is part of the
// distribution (JAR)
throw new RuntimeException("Unable to load default stopword set");
}
}
}
/**
* Builds an analyzer with the default stop words.
*
* @param matchVersion lucene compatibility version
*/
public ThaiAnalyzer(Version matchVersion) {
this(matchVersion, matchVersion.onOrAfter(Version.LUCENE_36) ? DefaultSetHolder.DEFAULT_STOP_SET : StopAnalyzer.ENGLISH_STOP_WORDS_SET);
}
/**
* Builds an analyzer with the given stop words.
*
* @param matchVersion lucene compatibility version
* @param stopwords a stopword set
*/
public ThaiAnalyzer(Version matchVersion, CharArraySet stopwords) {
super(matchVersion, stopwords);
}
/**
* Creates
* {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents}
* used to tokenize all the text in the provided {@link Reader}.
*
* @return {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents}
* built from a {@link StandardTokenizer} filtered with
* {@link StandardFilter}, {@link LowerCaseFilter}, {@link ThaiWordFilter}, and
* {@link StopFilter}
*/
@Override
protected TokenStreamComponents createComponents(String fieldName,
Reader reader) {
final Tokenizer source = new StandardTokenizer(matchVersion, reader);
TokenStream result = new StandardFilter(matchVersion, source);
if (matchVersion.onOrAfter(Version.LUCENE_31))
result = new LowerCaseFilter(matchVersion, result);
result = new ThaiWordFilter(matchVersion, result);
return new TokenStreamComponents(source, new StopFilter(matchVersion,
result, stopwords));
}
}