Package org.apache.lucene.analysis.cjk

Class CJKBigramFilter

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.TokenFilter

org.apache.lucene.analysis.cjk.CJKBigramFilter

All Implemented Interfaces:

Closeable, AutoCloseable

public final class CJKBigramFilter
extends TokenFilter

Forms bigrams of CJK terms that are generated from StandardTokenizer or ICUTokenizer.

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.

In all cases, all non-CJK input is passed thru unmodified.

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 String	DOUBLE_TYPE	when we emit a bigram, its then marked as this type
static final int	HAN	bigram flag for Han Ideographs
static final int	HANGUL	bigram flag for Hangul
static final int	HIRAGANA	bigram flag for Hiragana
static final int	KATAKANA	bigram flag for Katakana
static final String	SINGLE_TYPE	when we emit a unigram, its then marked as this type

Constructor Summary

Constructors

Constructor	Description
CJKBigramFilter(TokenStream in)	Calls CJKBigramFilter(in, HAN | HIRAGANA | KATAKANA | HANGUL)
CJKBigramFilter(TokenStream in, int flags)	Calls CJKBigramFilter(in, flags, false)
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 Type	Method	Description
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 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

HAN

public static final int HAN

bigram flag for Han Ideographs

See Also:

• Constant Field Values

HIRAGANA

public static final int HIRAGANA

bigram flag for Hiragana

See Also:

• Constant Field Values

KATAKANA

public static final int KATAKANA

bigram flag for Katakana

See Also:

• Constant Field Values

HANGUL

public static final int HANGUL

bigram flag for Hangul

See Also:

• Constant Field Values

DOUBLE_TYPE

public static final String DOUBLE_TYPE

when we emit a bigram, its then marked as this type

See Also:

• Constant Field Values

SINGLE_TYPE

public static final String SINGLE_TYPE

when we emit a unigram, its then marked as this type

See Also:

• Constant Field Values

Constructor Details

CJKBigramFilter

public CJKBigramFilter(TokenStream in)

Calls CJKBigramFilter(in, HAN | HIRAGANA | KATAKANA | HANGUL)

CJKBigramFilter

public CJKBigramFilter(TokenStream in,
 int flags)

Calls CJKBigramFilter(in, flags, false)

CJKBigramFilter

public 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.

Parameters:

flags - OR'ed set from HAN, HIRAGANA, KATAKANA, HANGUL

outputUnigrams - true if unigrams for the selected writing systems should also be output. when this is false, this is only done when there are no adjacent characters to form a bigram.

Method Details

incrementToken

public 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), 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().

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