Module org.apache.lucene.analysis.kuromoji
Package org.apache.lucene.analysis.ja

Class JapaneseKatakanaStemFilter

java.lang.Object
org.apache.lucene.util.AttributeSource
org.apache.lucene.analysis.TokenStream
org.apache.lucene.analysis.TokenFilter
org.apache.lucene.analysis.ja.JapaneseKatakanaStemFilter
All Implemented Interfaces:
Closeable, AutoCloseable, Unwrappable<TokenStream>
public final class JapaneseKatakanaStemFilter extends TokenFilter
A TokenFilter that normalizes common katakana spelling variations ending in a long sound character by removing this character (U+30FC). Only katakana words longer than a minimum length are stemmed (default is four).

Note that only full-width katakana characters are supported. Please use a CJKWidthFilter to convert half-width katakana to full-width before using this filter.

In order to prevent terms from being stemmed, use an instance of SetKeywordMarkerFilter or a custom TokenFilter that sets the KeywordAttribute before this TokenStream.

  • Field Details

    • DEFAULT_MINIMUM_LENGTH

      public static final int DEFAULT_MINIMUM_LENGTH
      See Also:

    • HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK

      private static final char HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK
      See Also:

    • termAttr

      private final CharTermAttribute termAttr

    • keywordAttr

      private final KeywordAttribute keywordAttr

    • minimumKatakanaLength

      private final int minimumKatakanaLength

  • Constructor Details

    • JapaneseKatakanaStemFilter

      public JapaneseKatakanaStemFilter(TokenStream input, int minimumLength)

    • JapaneseKatakanaStemFilter

      public JapaneseKatakanaStemFilter(TokenStream input)

  • Method Details

    • incrementToken

      public boolean incrementToken() throws IOException
      Description copied from class: TokenStream
      Consumers (i.e., IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate AttributeImpls with the attributes of the next token.

      The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use AttributeSource.captureState() to create a copy of the current attribute state.

      This method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to AttributeSource.addAttribute(Class) and AttributeSource.getAttribute(Class), references to all AttributeImpls that this stream uses should be retrieved during instantiation.

      To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in TokenStream.incrementToken().

      Specified by:
      incrementToken in class TokenStream
      Returns:
      false for end of stream; true otherwise
      Throws:
      IOException

    • stem

      private int stem(char[] term, int length)

    • isKatakana

      private boolean isKatakana(char[] term, int length)