org.apache.lucene.analysis.cjk.CJKAnalyzer.java Source code

Introduction

Here is the source code for org.apache.lucene.analysis.cjk.CJKAnalyzer.java

Source

/*
 * 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.cjk;

import java.io.IOException;

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.StopwordAnalyzerBase;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.standard.StandardTokenizer;

/**
 * An {@link Analyzer} that tokenizes text with {@link StandardTokenizer},
 * normalizes content with {@link CJKWidthFilter}, folds case with
 * {@link LowerCaseFilter}, forms bigrams of CJK with {@link CJKBigramFilter},
 * and filters stopwords with {@link StopFilter}
 *
 * @since 3.1
 */
public final class CJKAnalyzer extends StopwordAnalyzerBase {

    /**
     * File containing default CJK stopwords.
     * <p>
     * Currently it contains some common English words that are not usually
     * useful for searching and some double-byte interpunctions.
     */
    public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";

    /**
     * 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;
    }

    private static class DefaultSetHolder {
        static final CharArraySet DEFAULT_STOP_SET;

        static {
            try {
                DEFAULT_STOP_SET = loadStopwordSet(false, CJKAnalyzer.class, DEFAULT_STOPWORD_FILE, "#");
            } 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 which removes words in {@link #getDefaultStopSet()}.
     */
    public CJKAnalyzer() {
        this(DefaultSetHolder.DEFAULT_STOP_SET);
    }

    /**
     * Builds an analyzer with the given stop words
     * 
     * @param stopwords
     *          a stopword set
     */
    public CJKAnalyzer(CharArraySet stopwords) {
        super(stopwords);
    }

    @Override
    protected TokenStreamComponents createComponents(String fieldName) {
        final Tokenizer source = new StandardTokenizer();
        // run the widthfilter first before bigramming, it sometimes combines characters.
        TokenStream result = new CJKWidthFilter(source);
        result = new LowerCaseFilter(result);
        result = new CJKBigramFilter(result);
        return new TokenStreamComponents(source, new StopFilter(result, stopwords));
    }

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