+ * This analyzer implements light-stemming as specified by: Searching + * Strategies for the Bulgarian Language + * http://members.unine.ch/jacques.savoy/Papers/BUIR.pdf + *
+ */ +public final class BulgarianAnalyzer extends StopwordAnalyzerBase { + + /** + * File containing default Bulgarian stopwords. + * + * Default stopword list is from + * http://members.unine.ch/jacques.savoy/clef/index.html The stopword list is + * BSD-Licensed. + */ + public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt"; + + /** + * The comment character in the stopwords file. All lines prefixed with this + * will be ignored + * @deprecated use {@link WordlistLoader#getWordSet(Reader, String, Version)} directly + */ + //TODO make this private + @Deprecated + public static final String STOPWORDS_COMMENT = "#"; + + /** + * Returns an unmodifiable instance of the default stop-words set. + * + * @return an unmodifiable instance of the default stop-words set. + */ + public static Set 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 Set DEFAULT_STOP_SET; + + static { + try { + DEFAULT_STOP_SET = loadStopwordSet(false, BulgarianAnalyzer.class, DEFAULT_STOPWORD_FILE, STOPWORDS_COMMENT); + } 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"); + } + } + } + + private final Set stemExclusionSet; + + /** + * Builds an analyzer with the default stop words: + * {@link #DEFAULT_STOPWORD_FILE}. + */ + public BulgarianAnalyzer(Version matchVersion) { + this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET); + } + + /** + * Builds an analyzer with the given stop words. + */ + public BulgarianAnalyzer(Version matchVersion, Set stopwords) { + this(matchVersion, stopwords, CharArraySet.EMPTY_SET); + } + + /** + * Builds an analyzer with the given stop words and a stem exclusion set. + * If a stem exclusion set is provided this analyzer will add a {@link KeywordMarkerFilter} + * before {@link BulgarianStemFilter}. + */ + public BulgarianAnalyzer(Version matchVersion, Set stopwords, Set stemExclusionSet) { + super(matchVersion, stopwords); + this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy( + matchVersion, stemExclusionSet)); } + + /** + * Creates a + * {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents} + * which tokenizes all the text in the provided {@link Reader}. + * + * @return A + * {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents} + * built from an {@link StandardTokenizer} filtered with + * {@link StandardFilter}, {@link LowerCaseFilter}, {@link StopFilter} + * , {@link KeywordMarkerFilter} if a stem exclusion set is + * provided and {@link BulgarianStemFilter}. + */ + @Override + public TokenStreamComponents createComponents(String fieldName, Reader reader) { + final Tokenizer source = new StandardTokenizer(matchVersion, reader); + TokenStream result = new StandardFilter(matchVersion, source); + result = new LowerCaseFilter(matchVersion, result); + result = new StopFilter(matchVersion, result, stopwords); + if(!stemExclusionSet.isEmpty()) + result = new KeywordMarkerFilter(result, stemExclusionSet); + result = new BulgarianStemFilter(result); + return new TokenStreamComponents(source, result); + } +}