Class CJKBigramFilter

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, Unwrappable<TokenStream>

    public final class CJKBigramFilter
    extends TokenFilter
    Forms bigrams of CJK terms that are generated from StandardTokenizer or ICUTokenizer.

    CJK types are set by these tokenizers, but you can also use CJKBigramFilter(TokenStream, int) to explicitly control which of the CJK scripts are turned into bigrams.

    By default, when a CJK character has no adjacent characters to form a bigram, it is output in unigram form. If you want to always output both unigrams and bigrams, set the outputUnigrams flag in CJKBigramFilter(TokenStream, int, boolean). This can be used for a combined unigram+bigram approach.

    Unlike ICUTokenizer, StandardTokenizer does not split at script boundaries. Korean Hangul characters are treated the same as many other scripts' letters, and as a result, StandardTokenizer can produce tokens that mix Hangul and non-Hangul characters, e.g. "한국abc". Such mixed-script tokens are typed as <ALPHANUM> rather than <HANGUL>, and as a result, will not be converted to bigrams by CJKBigramFilter.

    In all cases, all non-CJK input is passed thru unmodified.

    • Field Detail

      • DOUBLE_TYPE

        public static final java.lang.String DOUBLE_TYPE
        when we emit a bigram, it's then marked as this type
        See Also:
        Constant Field Values
      • SINGLE_TYPE

        public static final java.lang.String SINGLE_TYPE
        when we emit a unigram, it's then marked as this type
        See Also:
        Constant Field Values
      • HAN_TYPE

        private static final java.lang.String HAN_TYPE
      • HIRAGANA_TYPE

        private static final java.lang.String HIRAGANA_TYPE
      • KATAKANA_TYPE

        private static final java.lang.String KATAKANA_TYPE
      • HANGUL_TYPE

        private static final java.lang.String HANGUL_TYPE
      • NO

        private static final java.lang.Object NO
      • doHan

        private final java.lang.Object doHan
      • doHiragana

        private final java.lang.Object doHiragana
      • doKatakana

        private final java.lang.Object doKatakana
      • doHangul

        private final java.lang.Object doHangul
      • outputUnigrams

        private final boolean outputUnigrams
      • ngramState

        private boolean ngramState
      • buffer

        int[] buffer
      • startOffset

        int[] startOffset
      • endOffset

        int[] endOffset
      • bufferLen

        int bufferLen
      • index

        int index
      • lastEndOffset

        int lastEndOffset
      • exhausted

        private boolean exhausted
    • 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
      • doNext

        private boolean doNext()
                        throws java.io.IOException
        looks at next input token, returning false is none is available
        Throws:
        java.io.IOException
      • refill

        private void refill()
        refills buffers with new data from the current token.
      • flushBigram

        private void flushBigram()
        Flushes a bigram token to output from our buffer This is the normal case, e.g. ABC -> AB BC
      • flushUnigram

        private void flushUnigram()
        Flushes a unigram token to output from our buffer. This happens when we encounter isolated CJK characters, either the whole CJK string is a single character, or we encounter a CJK character surrounded by space, punctuation, english, etc, but not beside any other CJK.
      • hasBufferedBigram

        private boolean hasBufferedBigram()
        True if we have multiple codepoints sitting in our buffer
      • hasBufferedUnigram

        private boolean hasBufferedUnigram()
        True if we have a single codepoint sitting in our buffer, where its future (whether it is emitted as unigram or forms a bigram) depends upon not-yet-seen inputs.
      • reset

        public void reset()
                   throws java.io.IOException
        Description copied from class: TokenFilter
        This method is called by a consumer before it begins consumption using TokenStream.incrementToken().

        Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.

        If you override this method, always call super.reset(), otherwise some internal state will not be correctly reset (e.g., Tokenizer will throw IllegalStateException on further usage).

        NOTE: The default implementation chains the call to the input TokenStream, so be sure to call super.reset() when overriding this method.

        Overrides:
        reset in class TokenFilter
        Throws:
        java.io.IOException