Class NGramTokenFilter
- java.lang.Object
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- org.apache.lucene.util.AttributeSource
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- org.apache.lucene.analysis.TokenStream
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- org.apache.lucene.analysis.TokenFilter
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- org.apache.lucene.analysis.ngram.NGramTokenFilter
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- All Implemented Interfaces:
java.io.Closeable
,java.lang.AutoCloseable
public final class NGramTokenFilter extends TokenFilter
Tokenizes the input into n-grams of the given size(s). As of Lucene 4.4, this token filter:- handles supplementary characters correctly,
- emits all n-grams for the same token at the same position,
- does not modify offsets,
- sorts n-grams by their offset in the original token first, then increasing length (meaning that "abc" will give "a", "ab", "abc", "b", "bc", "c").
If you were using this
TokenFilter
to perform partial highlighting, this won't work anymore since this filter doesn't update offsets. You should modify your analysis chain to useNGramTokenizer
, and potentially overrideNGramTokenizer.isTokenChar(int)
to perform pre-tokenization.
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Nested Class Summary
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Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
AttributeSource.State
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Field Summary
Fields Modifier and Type Field Description private int
curGramSize
private int
curPos
private int
curPosIncr
private char[]
curTermBuffer
private int
curTermCodePointCount
private int
curTermLength
static boolean
DEFAULT_PRESERVE_ORIGINAL
private int
maxGram
private int
minGram
private PositionIncrementAttribute
posIncrAtt
private boolean
preserveOriginal
private AttributeSource.State
state
private CharTermAttribute
termAtt
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Fields inherited from class org.apache.lucene.analysis.TokenFilter
input
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Fields inherited from class org.apache.lucene.analysis.TokenStream
DEFAULT_TOKEN_ATTRIBUTE_FACTORY
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Constructor Summary
Constructors Constructor Description NGramTokenFilter(TokenStream input, int gramSize)
Creates an NGramTokenFilter that produces n-grams of the indicated size.NGramTokenFilter(TokenStream input, int minGram, int maxGram, boolean preserveOriginal)
Creates an NGramTokenFilter that, for a given input term, produces all contained n-grams with lengths >= minGram and <= maxGram.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
end()
This method is called by the consumer after the last token has been consumed, afterTokenStream.incrementToken()
returnedfalse
(using the newTokenStream
API).boolean
incrementToken()
Consumers (i.e.,IndexWriter
) use this method to advance the stream to the next token.void
reset()
This method is called by a consumer before it begins consumption usingTokenStream.incrementToken()
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Methods inherited from class org.apache.lucene.analysis.TokenFilter
close
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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 Detail
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DEFAULT_PRESERVE_ORIGINAL
public static final boolean DEFAULT_PRESERVE_ORIGINAL
- See Also:
- Constant Field Values
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minGram
private final int minGram
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maxGram
private final int maxGram
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preserveOriginal
private final boolean preserveOriginal
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curTermBuffer
private char[] curTermBuffer
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curTermLength
private int curTermLength
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curTermCodePointCount
private int curTermCodePointCount
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curGramSize
private int curGramSize
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curPos
private int curPos
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curPosIncr
private int curPosIncr
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state
private AttributeSource.State state
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termAtt
private final CharTermAttribute termAtt
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posIncrAtt
private final PositionIncrementAttribute posIncrAtt
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Constructor Detail
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NGramTokenFilter
public NGramTokenFilter(TokenStream input, int minGram, int maxGram, boolean preserveOriginal)
Creates an NGramTokenFilter that, for a given input term, produces all contained n-grams with lengths >= minGram and <= maxGram. Will optionally preserve the original term when its length is outside of the defined range. Note: Care must be taken when choosing minGram and maxGram; depending on the input token size, this filter potentially produces a huge number of terms.- Parameters:
input
-TokenStream
holding the input to be tokenizedminGram
- the minimum length of the generated n-gramsmaxGram
- the maximum length of the generated n-gramspreserveOriginal
- Whether or not to keep the original term when it is shorter than minGram or longer than maxGram
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NGramTokenFilter
public NGramTokenFilter(TokenStream input, int gramSize)
Creates an NGramTokenFilter that produces n-grams of the indicated size.- Parameters:
input
-TokenStream
holding the input to be tokenizedgramSize
- the size of n-grams to generate.
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Method Detail
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incrementToken
public final 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 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:
java.io.IOException
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reset
public void reset() throws java.io.IOException
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:
java.io.IOException
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end
public void end() throws java.io.IOException
Description copied from class:TokenFilter
This method is called by the consumer after the last token has been consumed, afterTokenStream.incrementToken()
returnedfalse
(using the newTokenStream
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.
Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.
If you override this method, always call
super.end()
.NOTE: The default implementation chains the call to the input TokenStream, so be sure to call
super.end()
first when overriding this method.- Overrides:
end
in classTokenFilter
- Throws:
java.io.IOException
- If an I/O error occurs
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