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Apache Lucene (module: kuromoji)
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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.ja;

import java.io.IOException;
import java.io.Reader;
import java.io.UncheckedIOException;
import java.nio.charset.StandardCharsets;
import java.util.Set;
import java.util.stream.Collectors;
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.WordlistLoader;
import org.apache.lucene.analysis.cjk.CJKWidthCharFilter;
import org.apache.lucene.analysis.ja.JapaneseTokenizer.Mode;
import org.apache.lucene.analysis.ja.dict.UserDictionary;
import org.apache.lucene.util.IOUtils;

/**
 * Analyzer for Japanese that uses morphological analysis.
 *
 * @see JapaneseTokenizer
 * @since 3.6.0
 */
public class JapaneseAnalyzer extends StopwordAnalyzerBase {
  private final Mode mode;
  private final Set stoptags;
  private final UserDictionary userDict;

  public JapaneseAnalyzer() {
    this(
        null,
        JapaneseTokenizer.DEFAULT_MODE,
        DefaultSetHolder.DEFAULT_STOP_SET,
        DefaultSetHolder.DEFAULT_STOP_TAGS);
  }

  public JapaneseAnalyzer(
      UserDictionary userDict, Mode mode, CharArraySet stopwords, Set stoptags) {
    super(stopwords);
    this.userDict = userDict;
    this.mode = mode;
    this.stoptags = stoptags;
  }

  public static CharArraySet getDefaultStopSet() {
    return DefaultSetHolder.DEFAULT_STOP_SET;
  }

  public static Set getDefaultStopTags() {
    return DefaultSetHolder.DEFAULT_STOP_TAGS;
  }

  /**
   * Atomically loads DEFAULT_STOP_SET, DEFAULT_STOP_TAGS 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 final Set DEFAULT_STOP_TAGS;

    static {
      try {
        DEFAULT_STOP_SET =
            CharArraySet.unmodifiableSet(
                WordlistLoader.getWordSet(
                    IOUtils.getDecodingReader(
                        IOUtils.requireResourceNonNull(
                            JapaneseAnalyzer.class.getResourceAsStream("stopwords.txt"),
                            "stopwords.txt"),
                        StandardCharsets.UTF_8),
                    "#",
                    new CharArraySet(16, true))); // ignore case
        final CharArraySet tagset =
            WordlistLoader.getWordSet(
                IOUtils.requireResourceNonNull(
                    JapaneseAnalyzer.class.getResourceAsStream("stoptags.txt"), "stoptags.txt"),
                "#");
        DEFAULT_STOP_TAGS =
            tagset.stream()
                .map(ca -> new String((char[]) ca))
                .collect(Collectors.toUnmodifiableSet());
      } catch (IOException ex) {
        // default set should always be present as it is part of the distribution (JAR)
        throw new UncheckedIOException("Unable to load default stopword or stoptag set", ex);
      }
    }
  }

  @Override
  protected TokenStreamComponents createComponents(String fieldName) {
    Tokenizer tokenizer = new JapaneseTokenizer(userDict, true, true, mode);
    TokenStream stream = new JapaneseBaseFormFilter(tokenizer);
    stream = new JapanesePartOfSpeechStopFilter(stream, stoptags);
    stream = new StopFilter(stream, stopwords);
    stream = new JapaneseKatakanaStemFilter(stream);
    stream = new LowerCaseFilter(stream);
    return new TokenStreamComponents(tokenizer, stream);
  }

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

  @Override
  protected Reader initReader(String fieldName, Reader reader) {
    return new CJKWidthCharFilter(reader);
  }

  @Override
  protected Reader initReaderForNormalization(String fieldName, Reader reader) {
    return new CJKWidthCharFilter(reader);
  }
}