Package org.apache.lucene.analysis.ja

Class JapaneseKatakanaStemFilter

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable
    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 Detail

      • HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK

        private static final char HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK
        See Also:
        Constant Field Values

      • minimumKatakanaLength

        private final int minimumKatakanaLength

    • Constructor Detail

      • JapaneseKatakanaStemFilter

        public JapaneseKatakanaStemFilter​(TokenStream input,
                                  int minimumLength)

      • JapaneseKatakanaStemFilter

        public JapaneseKatakanaStemFilter​(TokenStream input)

    • Method Detail

      • incrementToken

        public boolean incrementToken()
                       throws java.io.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:
        java.io.IOException

      • stem

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

      • isKatakana

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