org.apache.lucene.analysis.ngram
Class EdgeNGramTokenFilter

java.lang.Object
  org.apache.lucene.util.AttributeSource
      org.apache.lucene.analysis.TokenStream
          org.apache.lucene.analysis.TokenFilter
              org.apache.lucene.analysis.ngram.EdgeNGramTokenFilter

public class EdgeNGramTokenFilter
extends TokenFilter

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

This TokenFilter create n-grams from the beginning edge or ending edge of a input token.

Nested Class Summary

static class

EdgeNGramTokenFilter.Side Specifies which side of the input the n-gram should be generated from

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

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

static int	DEFAULT_MAX_GRAM_SIZE
static int	DEFAULT_MIN_GRAM_SIZE
static EdgeNGramTokenFilter.Side	DEFAULT_SIDE

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

input

Constructor Summary

protected	EdgeNGramTokenFilter(TokenStream input)
	EdgeNGramTokenFilter(TokenStream input, EdgeNGramTokenFilter.Side side, int minGram, int maxGram) Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range
	EdgeNGramTokenFilter(TokenStream input, String sideLabel, int minGram, int maxGram) Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range

Method Summary

boolean	incrementToken() Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.
Token	next() Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.
Token	next(Token reusableToken) Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.
void	reset() Reset the filter as well as the input TokenStream.

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

close, end

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

getOnlyUseNewAPI, setOnlyUseNewAPI

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

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

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_SIDE

public static final EdgeNGramTokenFilter.Side DEFAULT_SIDE

DEFAULT_MAX_GRAM_SIZE

public static final int DEFAULT_MAX_GRAM_SIZE

See Also:

Constant Field Values

DEFAULT_MIN_GRAM_SIZE

public static final int DEFAULT_MIN_GRAM_SIZE

See Also:

Constant Field Values

Constructor Detail

EdgeNGramTokenFilter

protected EdgeNGramTokenFilter(TokenStream input)

EdgeNGramTokenFilter

public EdgeNGramTokenFilter(TokenStream input,
                            EdgeNGramTokenFilter.Side side,
                            int minGram,
                            int maxGram)

Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range

Parameters:

input - TokenStream holding the input to be tokenized

side - the EdgeNGramTokenFilter.Side from which to chop off an n-gram

minGram - the smallest n-gram to generate

maxGram - the largest n-gram to generate

EdgeNGramTokenFilter

public EdgeNGramTokenFilter(TokenStream input,
                            String sideLabel,
                            int minGram,
                            int maxGram)

Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range

Parameters:

input - TokenStream holding the input to be tokenized

sideLabel - the name of the EdgeNGramTokenFilter.Side from which to chop off an n-gram

minGram - the smallest n-gram to generate

maxGram - the largest n-gram to generate

Method Detail

incrementToken

public final 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) or downcasts, 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().

Overrides:

incrementToken in class TokenStream

Returns:

false for end of stream; true otherwise

Note that this method will be defined abstract in Lucene 3.0.

Throws:

IOException

next

public final Token next(Token reusableToken)
                 throws IOException

Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.

Description copied from class: TokenStream

Returns the next token in the stream, or null at EOS. When possible, the input Token should be used as the returned Token (this gives fastest tokenization performance), but this is not required and a new Token may be returned. Callers may re-use a single Token instance for successive calls to this method.

This implicitly defines a "contract" between consumers (callers of this method) and producers (implementations of this method that are the source for tokens):

• A consumer must fully consume the previously returned Token before calling this method again.
• A producer must call Token.clear() before setting the fields in it and returning it

Also, the producer must make no assumptions about a Token after it has been returned: the caller may arbitrarily change it. If the producer needs to hold onto the Token for subsequent calls, it must clone() it before storing it. Note that a TokenFilter is considered a consumer.

Overrides:

next in class TokenStream

Parameters:

reusableToken - a Token that may or may not be used to return; this parameter should never be null (the callee is not required to check for null before using it, but it is a good idea to assert that it is not null.)

Returns:

next Token in the stream or null if end-of-stream was hit

Throws:

IOException

next

public final Token next()
                 throws IOException

Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.

Description copied from class: TokenStream

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

Overrides:

next in class TokenStream

Throws:

IOException

reset

public void reset()
           throws IOException

Description copied from class: TokenFilter

Reset the filter as well as the input TokenStream.

Overrides:

reset in class TokenFilter

Throws:

IOException