Package org.apache.lucene.analysis.ngram

Class NGramTokenFilter

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.TokenFilter

org.apache.lucene.analysis.ngram.NGramTokenFilter

All Implemented Interfaces:

Closeable, AutoCloseable

public final class NGramTokenFilter
extends TokenFilter

Tokenizes the input into n-grams of the given size(s).

You must specify the required Version compatibility when creating a NGramTokenFilter. As of Lucene 4.4, this token filters:

• 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").

You can make this filter use the old behavior by providing a version < Version.LUCENE_44 in the constructor but this is not recommended as it will lead to broken TokenStreams that will cause highlighting bugs.

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 use NGramTokenizer, and potentially override NGramTokenizer.isTokenChar(int) to perform pre-tokenization.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_MAX_NGRAM_SIZE
static final int	DEFAULT_MIN_NGRAM_SIZE

Constructor Summary

Constructors

Constructor	Description
NGramTokenFilter(Version version, TokenStream input)	Creates NGramTokenFilter with default min and max n-grams.
NGramTokenFilter(Version version, TokenStream input, int minGram, int maxGram)	Creates NGramTokenFilter with given min and max n-grams.

Method Summary

Modifier and Type	Method	Description
final boolean	incrementToken()	Returns the next token in the stream, or null at EOS.
void	reset()	This method is called by a consumer before it begins consumption using TokenStream.incrementToken().

Methods inherited from class org.apache.lucene.analysis.TokenFilter

close, end

Methods inherited from class org.apache.lucene.util.AttributeSource

addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Field Details

DEFAULT_MIN_NGRAM_SIZE

public static final int DEFAULT_MIN_NGRAM_SIZE

See Also:

• Constant Field Values

DEFAULT_MAX_NGRAM_SIZE

public static final int DEFAULT_MAX_NGRAM_SIZE

See Also:

• Constant Field Values

Constructor Details

NGramTokenFilter

public NGramTokenFilter(Version version,
 TokenStream input,
 int minGram,
 int maxGram)

Creates NGramTokenFilter with given min and max n-grams.

Parameters:

version - Lucene version to enable correct position increments. See above for details.

input - TokenStream holding the input to be tokenized

minGram - the smallest n-gram to generate

maxGram - the largest n-gram to generate

NGramTokenFilter

public NGramTokenFilter(Version version,
 TokenStream input)

Creates NGramTokenFilter with default min and max n-grams.

Parameters:

version - Lucene version to enable correct position increments. See above for details.

input - TokenStream holding the input to be tokenized

Method Details

incrementToken

public final boolean incrementToken()
                             throws IOException

Returns the next token in the stream, or null at EOS.

Specified by:

incrementToken in class TokenStream

Returns:

false for end of stream; true otherwise

Throws:

IOException

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