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 * 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
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 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.lucene.analysis.de;
// This file is encoded in UTF-8


import java.io.IOException;
import java.io.Reader;
import java.nio.charset.StandardCharsets;

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.WordlistLoader;
import org.apache.lucene.analysis.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.snowball.SnowballFilter;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.IOUtils;

Analyzer for German language. 

Supports an external list of stopwords (words that
will not be indexed at all) and an external list of exclusions (word that will
not be stemmed, but indexed).
A default set of stopwords is used unless an alternative list is specified, but the
exclusion list is empty by default.

NOTE: This class uses the same Version dependent settings as StandardAnalyzer.
Since:
3.1/**
 * {@link Analyzer} for German language. 
 * <p>
 * Supports an external list of stopwords (words that
 * will not be indexed at all) and an external list of exclusions (word that will
 * not be stemmed, but indexed).
 * A default set of stopwords is used unless an alternative list is specified, but the
 * exclusion list is empty by default.
 * </p>
 * 
 * <p><b>NOTE</b>: This class uses the same {@link org.apache.lucene.util.Version}
 * dependent settings as {@link StandardAnalyzer}.</p>
 *
 * @since 3.1
 */
public final class GermanAnalyzer extends StopwordAnalyzerBase {
  
  
File containing default German stopwords. /** File containing default German stopwords. */
  public final static String DEFAULT_STOPWORD_FILE = "german_stop.txt";
  
  
Returns a set of default German-stopwords 
Returns:
a set of default German-stopwords/**
   * Returns a set of default German-stopwords 
   * @return a set of default German-stopwords 
   */
  public static final CharArraySet getDefaultStopSet(){
    return DefaultSetHolder.DEFAULT_SET;
  }
  
  private static class DefaultSetHolder {
    private static final CharArraySet DEFAULT_SET;
    static {
      try {
        DEFAULT_SET = WordlistLoader.getSnowballWordSet(IOUtils.getDecodingReader(SnowballFilter.class, 
            DEFAULT_STOPWORD_FILE, StandardCharsets.UTF_8));
      } 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");
      }
    }
  }

  /**
   * Contains the stopwords used with the {@link StopFilter}.
   */
 
  
Contains words that should be indexed but not stemmed.
/**
   * Contains words that should be indexed but not stemmed.
   */
  private final CharArraySet exclusionSet;

  
Builds an analyzer with the default stop words: getDefaultStopSet(). /**
   * Builds an analyzer with the default stop words:
   * {@link #getDefaultStopSet()}.
   */
  public GermanAnalyzer() {
    this(DefaultSetHolder.DEFAULT_SET);
  }
  
  
Builds an analyzer with the given stop words 
Params:
stopwords – 
         a stopword set/**
   * Builds an analyzer with the given stop words 
   * 
   * @param stopwords
   *          a stopword set
   */
  public GermanAnalyzer(CharArraySet stopwords) {
    this(stopwords, CharArraySet.EMPTY_SET);
  }
  
  
Builds an analyzer with the given stop words
Params:
stopwords – 
         a stopword set
stemExclusionSet – 
         a stemming exclusion set/**
   * Builds an analyzer with the given stop words
   * 
   * @param stopwords
   *          a stopword set
   * @param stemExclusionSet
   *          a stemming exclusion set
   */
  public GermanAnalyzer(CharArraySet stopwords, CharArraySet stemExclusionSet) {
    super(stopwords);
    exclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(stemExclusionSet));
  }

  
Creates TokenStreamComponents used to tokenize all the text in the provided Reader. 
Returns:
TokenStreamComponents built from a StandardTokenizer filtered with LowerCaseFilter, StopFilter , SetKeywordMarkerFilter if a stem exclusion set is provided, GermanNormalizationFilter and GermanLightStemFilter/**
   * 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 LowerCaseFilter}, {@link StopFilter}
   *         , {@link SetKeywordMarkerFilter} if a stem exclusion set is
   *         provided, {@link GermanNormalizationFilter} and {@link GermanLightStemFilter}
   */
  @Override
  protected TokenStreamComponents createComponents(String fieldName) {
    final Tokenizer source = new StandardTokenizer();
    TokenStream result = new LowerCaseFilter(source);
    result = new StopFilter(result, stopwords);
    result = new SetKeywordMarkerFilter(result, exclusionSet);
    result = new GermanNormalizationFilter(result);
    result = new GermanLightStemFilter(result);
    return new TokenStreamComponents(source, result);
  }

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