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). 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 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.State

Field Summary

Fields

Modifier and Type	Field and Description
static boolean	DEFAULT_PRESERVE_ORIGINAL

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

input

Fields inherited from class org.apache.lucene.analysis.TokenStream

DEFAULT_TOKEN_ATTRIBUTE_FACTORY

Constructor Summary

Constructors

Constructor and 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.

Method Summary

Modifier and Type	Method and Description
void	end()
boolean	incrementToken()
void	reset()

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

close

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

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

DEFAULT_PRESERVE_ORIGINAL

public static final boolean DEFAULT_PRESERVE_ORIGINAL

See Also:

Constant Field Values

Constructor Detail

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 tokenized

minGram - the minimum length of the generated n-grams

maxGram - the maximum length of the generated n-grams

preserveOriginal - Whether or not to keep the original term when it is shorter than minGram or longer than maxGram

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 tokenized

gramSize - the size of n-grams to generate.

Method Detail

incrementToken

public final boolean incrementToken()
                             throws IOException

Specified by:

incrementToken in class TokenStream

Throws:

IOException

reset

public void reset()
           throws IOException

Overrides:

reset in class TokenFilter

Throws:

IOException

end

public void end()
         throws IOException

Overrides:

end in class TokenFilter

Throws:

IOException