org.apache.lucene.analysis.cn.smart.SmartChineseAnalyzer.java Source code

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Here is the source code for org.apache.lucene.analysis.cn.smart.SmartChineseAnalyzer.java

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/*
 * 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.nio.charset.StandardCharsets;
import java.util.Set;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.StopFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.WordlistLoader;
import org.apache.lucene.analysis.en.PorterStemFilter;
import org.apache.lucene.util.IOUtils;

/**
 * <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
 *
 * @since 3.1
 */
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, StandardCharsets.UTF_8), STOPWORD_FILE_COMMENT));
        }
    }

    /**
     * Create a new SmartChineseAnalyzer, using the default stopword list.
     */
    public SmartChineseAnalyzer() {
        this(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(boolean useDefaultStopWords) {
        stopWords = useDefaultStopWords ? DefaultSetHolder.DEFAULT_STOP_SET : CharArraySet.EMPTY_SET;
    }

    /**
     * <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(CharArraySet stopWords) {
        this.stopWords = stopWords == null ? CharArraySet.EMPTY_SET : stopWords;
    }

    @Override
    public TokenStreamComponents createComponents(String fieldName) {
        final Tokenizer tokenizer = new HMMChineseTokenizer();
        TokenStream result = 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(result, stopWords);
        }
        return new TokenStreamComponents(tokenizer, result);
    }

    @Override
    protected TokenStream normalize(String fieldName, TokenStream in) {
        return new LowerCaseFilter(in);
    }
}