org.apache.lucene.analysis.ja

Class JapaneseTokenizer

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.Tokenizer

org.apache.lucene.analysis.ja.JapaneseTokenizer

All Implemented Interfaces:

Closeable, AutoCloseable

public final class JapaneseTokenizer
extends Tokenizer

Tokenizer for Japanese that uses morphological analysis.

This tokenizer sets a number of additional attributes:

• BaseFormAttribute containing base form for inflected adjectives and verbs.
• PartOfSpeechAttribute containing part-of-speech.
• ReadingAttribute containing reading and pronunciation.
• InflectionAttribute containing additional part-of-speech information for inflected forms.

This tokenizer uses a rolling Viterbi search to find the least cost segmentation (path) of the incoming characters. For tokens that appear to be compound (> length 2 for all Kanji, or > length 7 for non-Kanji), we see if there is a 2nd best segmentation of that token after applying penalties to the long tokens. If so, and the Mode is JapaneseTokenizer.Mode.SEARCH, we output the alternate segmentation as well.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	JapaneseTokenizer.Mode Tokenization mode: this determines how the tokenizer handles compound and unknown words.

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

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

Fields

Modifier and Type	Field and Description
static JapaneseTokenizer.Mode	DEFAULT_MODE Default tokenization mode.

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

input

Constructor Summary

Constructors

Constructor and Description
JapaneseTokenizer(Reader input, UserDictionary userDictionary, boolean discardPunctuation, JapaneseTokenizer.Mode mode) Create a new JapaneseTokenizer.

Method Summary

Methods

Modifier and Type	Method and Description
void	end() This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API).
boolean	incrementToken() Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.
void	reset() Resets this stream to the beginning.
void	reset(Reader input) Expert: Reset the tokenizer to a new reader.
void	setGraphvizFormatter(GraphvizFormatter dotOut) Expert: set this to produce graphviz (dot) output of the Viterbi lattice

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

close, correctOffset

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

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

Field Detail

DEFAULT_MODE

public static final JapaneseTokenizer.Mode DEFAULT_MODE

Default tokenization mode. Currently this is JapaneseTokenizer.Mode.SEARCH.

Constructor Detail

JapaneseTokenizer

public JapaneseTokenizer(Reader input,
                 UserDictionary userDictionary,
                 boolean discardPunctuation,
                 JapaneseTokenizer.Mode mode)

Create a new JapaneseTokenizer.

Parameters:

input - Reader containing text

userDictionary - Optional: if non-null, user dictionary.

discardPunctuation - true if punctuation tokens should be dropped from the output.

mode - tokenization mode.

Method Detail

setGraphvizFormatter

public void setGraphvizFormatter(GraphvizFormatter dotOut)

Expert: set this to produce graphviz (dot) output of the Viterbi lattice

reset

public void reset(Reader input)
           throws IOException

Description copied from class: Tokenizer

Expert: Reset the tokenizer to a new reader. Typically, an analyzer (in its reusableTokenStream method) will use this to re-use a previously created tokenizer.

Overrides:

reset in class Tokenizer

Throws:

IOException

reset

public void reset()
           throws IOException

Description copied from class: TokenStream

Resets this stream to the beginning. This is an optional operation, so subclasses may or may not implement this method. TokenStream.reset() is not needed for the standard indexing process. However, if the tokens of a TokenStream are intended to be consumed more than once, it is necessary to implement TokenStream.reset(). Note that if your TokenStream caches tokens and feeds them back again after a reset, it is imperative that you clone the tokens when you store them away (on the first pass) as well as when you return them (on future passes after TokenStream.reset()).

Overrides:

reset in class TokenStream

Throws:

IOException

end

public void end()

Description copied from class: TokenStream

This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream 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.

Overrides:

end in class TokenStream

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