Package org.apache.lucene.analysis.ja

Class JapaneseTokenizer

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    public final class JapaneseTokenizer
extends Tokenizer
    Tokenizer for Japanese that uses morphological analysis.

    This tokenizer sets a number of additional attributes:

    This tokenizer uses a rolling Viterbi search to find the least cost segmentation (path) of the incoming characters. For tokens that appear to be compound (> length 2 for all Kanji, or > length 7 for non-Kanji), we see if there is a 2nd best segmentation of that token after applying penalties to the long tokens. If so, and the Mode is JapaneseTokenizer.Mode.SEARCH, we output the alternate segmentation as well.

    • Constructor Detail

      • JapaneseTokenizer

        public JapaneseTokenizer​(Reader input,
                         UserDictionary userDictionary,
                         boolean discardPunctuation,
                         JapaneseTokenizer.Mode mode)
        Create a new JapaneseTokenizer.
        Parameters:
        input - Reader containing text
        userDictionary - Optional: if non-null, user dictionary.
        discardPunctuation - true if punctuation tokens should be dropped from the output.
        mode - tokenization mode.

    • Method Detail

      • setGraphvizFormatter

        public void setGraphvizFormatter​(GraphvizFormatter dotOut)
        Expert: set this to produce graphviz (dot) output of the Viterbi lattice

      • reset

        public void reset​(Reader input)
           throws IOException
        Description copied from class: Tokenizer
        Expert: Reset the tokenizer to a new reader. Typically, an analyzer (in its reusableTokenStream method) will use this to re-use a previously created tokenizer.
        Overrides:
        reset in class Tokenizer
        Throws:
        IOException

      • reset

        public void reset()
           throws IOException
        Description copied from class: TokenStream
        Resets this stream to the beginning. This is an optional operation, so subclasses may or may not implement this method. TokenStream.reset() is not needed for the standard indexing process. However, if the tokens of a TokenStream are intended to be consumed more than once, it is necessary to implement TokenStream.reset(). Note that if your TokenStream caches tokens and feeds them back again after a reset, it is imperative that you clone the tokens when you store them away (on the first pass) as well as when you return them (on future passes after TokenStream.reset()).
        Overrides:
        reset in class TokenStream
        Throws:
        IOException

      • end

        public void end()
        Description copied from class: TokenStream
        This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API). Streams implementing the old API should upgrade to use this feature.

        This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

        Overrides:
        end in class TokenStream

      • 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