Class CJKBigramFilter

All Implemented Interfaces:
Closeable, 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 Details

    • HAN

      public static final int HAN
      bigram flag for Han Ideographs
      See Also:
    • HIRAGANA

      public static final int HIRAGANA
      bigram flag for Hiragana
      See Also:
    • KATAKANA

      public static final int KATAKANA
      bigram flag for Katakana
      See Also:
    • HANGUL

      public static final int HANGUL
      bigram flag for Hangul
      See Also:
    • DOUBLE_TYPE

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

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

      private static final String HAN_TYPE
    • HIRAGANA_TYPE

      private static final String HIRAGANA_TYPE
    • KATAKANA_TYPE

      private static final String KATAKANA_TYPE
    • HANGUL_TYPE

      private static final String HANGUL_TYPE
    • NO

      private static final Object NO
    • doHan

      private final Object doHan
    • doHiragana

      private final Object doHiragana
    • doKatakana

      private final Object doKatakana
    • doHangul

      private final Object doHangul
    • outputUnigrams

      private final boolean outputUnigrams
    • ngramState

      private boolean ngramState
    • termAtt

      private final CharTermAttribute termAtt
    • typeAtt

      private final TypeAttribute typeAtt
    • offsetAtt

      private final OffsetAttribute offsetAtt
    • posIncAtt

      private final PositionIncrementAttribute posIncAtt
    • posLengthAtt

      private final PositionLengthAttribute posLengthAtt
    • buffer

      int[] buffer
    • startOffset

      int[] startOffset
    • endOffset

      int[] endOffset
    • bufferLen

      int bufferLen
    • index

      int index
    • lastEndOffset

      int lastEndOffset
    • exhausted

      private boolean exhausted
    • loneState

      private AttributeSource.State loneState
  • Constructor Details

  • 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
    • doNext

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