Class CJKBigramFilter
- All Implemented Interfaces:
Closeable
,AutoCloseable
,Unwrappable<TokenStream>
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.
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Nested Class Summary
Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
AttributeSource.State
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Field Summary
FieldsModifier and TypeFieldDescription(package private) int[]
(package private) int
private final Object
private final Object
private final Object
private final Object
static final String
when we emit a bigram, it's then marked as this type(package private) int[]
private boolean
static final int
bigram flag for Han Ideographsprivate static final String
static final int
bigram flag for Hangulprivate static final String
static final int
bigram flag for Hiraganaprivate static final String
(package private) int
static final int
bigram flag for Katakanaprivate static final String
(package private) int
private AttributeSource.State
private boolean
private static final Object
private final OffsetAttribute
private final boolean
private final PositionIncrementAttribute
private final PositionLengthAttribute
static final String
when we emit a unigram, it's then marked as this type(package private) int[]
private final CharTermAttribute
private final TypeAttribute
Fields inherited from class org.apache.lucene.analysis.TokenFilter
input
Fields inherited from class org.apache.lucene.analysis.TokenStream
DEFAULT_TOKEN_ATTRIBUTE_FACTORY
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Constructor Summary
ConstructorsConstructorDescriptionCJKBigramFilter
(TokenStream in, int flags) CJKBigramFilter
(TokenStream in, int flags, boolean outputUnigrams) Create a new CJKBigramFilter, specifying which writing systems should be bigrammed, and whether or not unigrams should also be output. -
Method Summary
Modifier and TypeMethodDescriptionprivate boolean
doNext()
looks at next input token, returning false is none is availableprivate void
Flushes a bigram token to output from our buffer This is the normal case, e.g.private void
Flushes a unigram token to output from our buffer.private boolean
True if we have multiple codepoints sitting in our bufferprivate boolean
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.boolean
Consumers (i.e.,IndexWriter
) use this method to advance the stream to the next token.private void
refill()
refills buffers with new data from the current token.void
reset()
This method is called by a consumer before it begins consumption usingTokenStream.incrementToken()
.Methods inherited from class org.apache.lucene.analysis.TokenFilter
close, end, unwrap
Methods inherited from class org.apache.lucene.util.AttributeSource
addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, endAttributes, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, removeAllAttributes, restoreState, toString
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Field Details
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HAN
public static final int HANbigram flag for Han Ideographs- See Also:
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HIRAGANA
public static final int HIRAGANAbigram flag for Hiragana- See Also:
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KATAKANA
public static final int KATAKANAbigram flag for Katakana- See Also:
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HANGUL
public static final int HANGULbigram flag for Hangul- See Also:
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DOUBLE_TYPE
when we emit a bigram, it's then marked as this type- See Also:
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SINGLE_TYPE
when we emit a unigram, it's then marked as this type- See Also:
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HAN_TYPE
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HIRAGANA_TYPE
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KATAKANA_TYPE
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HANGUL_TYPE
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NO
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doHan
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doHiragana
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doKatakana
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doHangul
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outputUnigrams
private final boolean outputUnigrams -
ngramState
private boolean ngramState -
termAtt
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typeAtt
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offsetAtt
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posIncAtt
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posLengthAtt
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buffer
int[] buffer -
startOffset
int[] startOffset -
endOffset
int[] endOffset -
bufferLen
int bufferLen -
index
int index -
lastEndOffset
int lastEndOffset -
exhausted
private boolean exhausted -
loneState
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Constructor Details
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CJKBigramFilter
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CJKBigramFilter
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CJKBigramFilter
Create a new CJKBigramFilter, specifying which writing systems should be bigrammed, and whether or not unigrams should also be output.
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Method Details
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incrementToken
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 appropriateAttributeImpl
s 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)
andAttributeSource.getAttribute(Class)
, references to allAttributeImpl
s 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 classTokenStream
- Returns:
- false for end of stream; true otherwise
- Throws:
IOException
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doNext
looks at next input token, returning false is none is available- Throws:
IOException
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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
Description copied from class:TokenFilter
This method is called by a consumer before it begins consumption usingTokenStream.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 throwIllegalStateException
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 classTokenFilter
- Throws:
IOException
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