/*
* 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.
*/
package org.apache.lucene.analysis.cn.smart;
import java.io.IOException;
import java.io.Reader;
import java.util.Set;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.en.PorterStemFilter;
import org.apache.lucene.analysis.util.CharArraySet;
import org.apache.lucene.analysis.util.WordlistLoader;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.cn.smart.SentenceTokenizer;
import org.apache.lucene.analysis.cn.smart.WordTokenFilter;
import org.apache.lucene.analysis.core.StopFilter;
import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.Version;
/**
* <p>
* SmartChineseAnalyzer is an analyzer for Chinese or mixed Chinese-English text.
* The analyzer uses probabilistic knowledge to find the optimal word segmentation for Simplified Chinese text.
* The text is first broken into sentences, then each sentence is segmented into words.
* </p>
* <p>
* Segmentation is based upon the <a href="http://en.wikipedia.org/wiki/Hidden_Markov_Model">Hidden Markov Model</a>.
* A large training corpus was used to calculate Chinese word frequency probability.
* </p>
* <p>
* This analyzer requires a dictionary to provide statistical data.
* SmartChineseAnalyzer has an included dictionary out-of-box.
* </p>
* <p>
* The included dictionary data is from <a href="http://www.ictclas.org">ICTCLAS1.0</a>.
* Thanks to ICTCLAS for their hard work, and for contributing the data under the Apache 2 License!
* </p>
* @lucene.experimental
*/
public final class SmartChineseAnalyzer extends Analyzer {
private final CharArraySet stopWords;
private static final String DEFAULT_STOPWORD_FILE = "stopwords.txt";
private static final String STOPWORD_FILE_COMMENT = "//";
/**
* Returns an unmodifiable instance of the default stop-words set.
* @return an unmodifiable instance of the 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 = loadDefaultStopWordSet();
} 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");
}
}
static CharArraySet loadDefaultStopWordSet() throws IOException {
// make sure it is unmodifiable as we expose it in the outer class
return CharArraySet.unmodifiableSet(WordlistLoader.getWordSet(IOUtils
.getDecodingReader(SmartChineseAnalyzer.class, DEFAULT_STOPWORD_FILE,
IOUtils.CHARSET_UTF_8), STOPWORD_FILE_COMMENT,
Version.LUCENE_CURRENT));
}
}
private final Version matchVersion;
/**
* Create a new SmartChineseAnalyzer, using the default stopword list.
*/
public SmartChineseAnalyzer(Version matchVersion) {
this(matchVersion, true);
}
/**
* <p>
* Create a new SmartChineseAnalyzer, optionally using the default stopword list.
* </p>
* <p>
* The included default stopword list is simply a list of punctuation.
* If you do not use this list, punctuation will not be removed from the text!
* </p>
*
* @param useDefaultStopWords true to use the default stopword list.
*/
public SmartChineseAnalyzer(Version matchVersion, boolean useDefaultStopWords) {
stopWords = useDefaultStopWords ? DefaultSetHolder.DEFAULT_STOP_SET
: CharArraySet.EMPTY_SET;
this.matchVersion = matchVersion;
}
/**
* <p>
* Create a new SmartChineseAnalyzer, using the provided {@link Set} of stopwords.
* </p>
* <p>
* Note: the set should include punctuation, unless you want to index punctuation!
* </p>
* @param stopWords {@link Set} of stopwords to use.
*/
public SmartChineseAnalyzer(Version matchVersion, CharArraySet stopWords) {
this.stopWords = stopWords==null?CharArraySet.EMPTY_SET:stopWords;
this.matchVersion = matchVersion;
}
@Override
public TokenStreamComponents createComponents(String fieldName, Reader reader) {
Tokenizer tokenizer = new SentenceTokenizer(reader);
TokenStream result = new WordTokenFilter(tokenizer);
// result = new LowerCaseFilter(result);
// LowerCaseFilter is not needed, as SegTokenFilter lowercases Basic Latin text.
// The porter stemming is too strict, this is not a bug, this is a feature:)
result = new PorterStemFilter(result);
if (!stopWords.isEmpty()) {
result = new StopFilter(matchVersion, result, stopWords);
}
return new TokenStreamComponents(tokenizer, result);
}
}