A TokenStream enumerates the sequence of tokens, either from Fields of a Document or from query text. This is an abstract class. Concrete subclasses are:

Tokenizer, a TokenStream whose input is a Reader; and
TokenFilter, a TokenStream whose input is another TokenStream.

A new TokenStream API has been introduced with Lucene 2.9. This API has moved from being Token based to IAttribute based. While Token still exists in 2.9 as a convenience class, the preferred way to store the information of a Token is to use Util.Attributes. TokenStream now extends AttributeSource, which provides access to all of the token IAttributes for the TokenStream. Note that only one instance per Util.Attribute is created and reused for every token. This approach reduces object creation and allows local caching of references to the Util.Attributes. See IncrementToken() for further details. The workflow of the new TokenStream API is as follows:

Instantiation of TokenStream/TokenFilters which add/get attributes to/from the AttributeSource.
The consumer calls TokenStream.Reset().
The consumer retrieves attributes from the stream and stores local references to all attributes it wants to access
The consumer calls IncrementToken() until it returns false and consumes the attributes after each call.
The consumer calls End() so that any end-of-stream operations can be performed.
The consumer calls Close() to release any resource when finished using the TokenStream

To make sure 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 IncrementToken(). You can find some example code for the new API in the analysis package level Javadoc. Sometimes it is desirable to capture a current state of a TokenStream , e. g. for buffering purposes (see CachingTokenFilter, TeeSinkTokenFilter). For this usecase AttributeSource.CaptureState and AttributeSource.RestoreState can be used. More...

Inherits Lucene.Net.Util.AttributeSource, and IDisposable.

Public Member Functions
abstract bool	IncrementToken ()
	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 Util.Attributes with the attributes of the next token.

virtual void	End ()
	This method is called by the consumer after the last token has been consumed, after 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.

virtual void	Reset ()
	Resets this stream to the beginning. This is an optional operation, so subclasses may or may not implement this method. 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 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 Reset()).

void	Close ()
	Releases resources associated with this stream.

void	Dispose ()

Public Member Functions inherited from Lucene.Net.Util.AttributeSource
	AttributeSource ()
	An AttributeSource using the default attribute factory AttributeSource.AttributeFactory.DEFAULT_ATTRIBUTE_FACTORY.

	AttributeSource (AttributeSource input)
	An AttributeSource that uses the same attributes as the supplied one.

	AttributeSource (AttributeFactory factory)
	An AttributeSource using the supplied AttributeFactory for creating new IAttribute instances.

virtual IEnumerable< Type >	GetAttributeTypesIterator ()
	Returns a new iterator that iterates the attribute classes in the same order they were added in. Signature for Java 1.5: `public Iterator<Class<? extends Attribute>> getAttributeClassesIterator()`

virtual IEnumerable< Attribute >	GetAttributeImplsIterator ()
	Returns a new iterator that iterates all unique Attribute implementations. This iterator may contain less entries that GetAttributeTypesIterator, if one instance implements more than one Attribute interface. Signature for Java 1.5: `public Iterator<AttributeImpl> getAttributeImplsIterator()`

virtual void	AddAttributeImpl (Attribute att)
	Expert: Adds a custom AttributeImpl instance with one or more Attribute interfaces.

virtual T	AddAttribute< T > ()
	The caller must pass in a Class<? extends Attribute> value. This method first checks if an instance of that class is already in this AttributeSource and returns it. Otherwise a new instance is created, added to this AttributeSource and returned.

virtual bool	HasAttribute< T > ()
	The caller must pass in a Class<? extends Attribute> value. Returns true, iff this AttributeSource contains the passed-in Attribute.

virtual T	GetAttribute< T > ()
	The caller must pass in a Class<? extends Attribute> value. Returns the instance of the passed in Attribute contained in this AttributeSource

virtual void	ClearAttributes ()
	Resets all Attributes in this AttributeSource by calling Attribute.Clear() on each Attribute implementation.

virtual State	CaptureState ()
	Captures the state of all Attributes. The return value can be passed to RestoreState to restore the state of this or another AttributeSource.

virtual void	RestoreState (State state)
	Restores this state by copying the values of all attribute implementations that this state contains into the attributes implementations of the targetStream. The targetStream must contain a corresponding instance for each argument contained in this state (e.g. it is not possible to restore the state of an AttributeSource containing a TermAttribute into a AttributeSource using a Token instance as implementation).

override int	GetHashCode ()

override bool	Equals (System.Object obj)

override System.String	ToString ()

virtual AttributeSource	CloneAttributes ()
	Performs a clone of all Attribute instances returned in a new AttributeSource instance. This method can be used to e.g. create another TokenStream with exactly the same attributes (using AttributeSource(AttributeSource))

Protected Member Functions
abstract void	Dispose (bool disposing)

Additional Inherited Members
Properties inherited from Lucene.Net.Util.AttributeSource
virtual AttributeFactory	Factory `[get]`
	Returns the used AttributeFactory.

virtual bool	HasAttributes `[get]`
	Returns true, iff this AttributeSource has any attributes

Detailed Description

A TokenStream enumerates the sequence of tokens, either from Fields of a Document or from query text.

This is an abstract class. Concrete subclasses are:

Tokenizer, a TokenStream whose input is a Reader; and
TokenFilter, a TokenStream whose input is another TokenStream.

A new TokenStream API has been introduced with Lucene 2.9. This API has moved from being Token based to IAttribute based. While Token still exists in 2.9 as a convenience class, the preferred way to store the information of a Token is to use Util.Attributes.

TokenStream now extends AttributeSource, which provides access to all of the token IAttributes for the TokenStream. Note that only one instance per Util.Attribute is created and reused for every token. This approach reduces object creation and allows local caching of references to the Util.Attributes. See IncrementToken() for further details.

The workflow of the new TokenStream API is as follows:

Instantiation of TokenStream/TokenFilters which add/get attributes to/from the AttributeSource.
The consumer calls TokenStream.Reset().
The consumer retrieves attributes from the stream and stores local references to all attributes it wants to access
The consumer calls IncrementToken() until it returns false and consumes the attributes after each call.
The consumer calls End() so that any end-of-stream operations can be performed.
The consumer calls Close() to release any resource when finished using the TokenStream

To make sure 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 IncrementToken().

You can find some example code for the new API in the analysis package level Javadoc.

Sometimes it is desirable to capture a current state of a TokenStream , e. g. for buffering purposes (see CachingTokenFilter, TeeSinkTokenFilter). For this usecase AttributeSource.CaptureState and AttributeSource.RestoreState can be used.

Definition at line 77 of file TokenStream.cs.

Member Function Documentation

void Lucene.Net.Analysis.TokenStream.Close ( )

Releases resources associated with this stream.

Definition at line 150 of file TokenStream.cs.

void Lucene.Net.Analysis.TokenStream.Dispose ( )

Definition at line 155 of file TokenStream.cs.

abstract void Lucene.Net.Analysis.TokenStream.Dispose ( bool disposing )

protectedpure virtual

virtual void Lucene.Net.Analysis.TokenStream.End ( )

virtual

This method is called by the consumer after the last token has been consumed, after 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.

<throws> IOException </throws>

Reimplemented in Lucene.Net.Analysis.CJK.CJKTokenizer, Lucene.Net.Analysis.TeeSinkTokenFilter.SinkTokenStream, Lucene.Net.Analysis.Standard.StandardTokenizer, Lucene.Net.Analysis.NGram.EdgeNGramTokenizer, Lucene.Net.Analysis.Cn.ChineseTokenizer, Lucene.Net.Analysis.TeeSinkTokenFilter, Lucene.Net.Analysis.NGram.NGramTokenizer, Lucene.Net.Analysis.CharTokenizer, Lucene.Net.Analysis.KeywordTokenizer, Lucene.Net.Analysis.CachingTokenFilter, and Lucene.Net.Analysis.TokenFilter.

Definition at line 130 of file TokenStream.cs.

abstract bool Lucene.Net.Analysis.TokenStream.IncrementToken ( )

pure virtual

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 Util.Attributes 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{T}() and AttributeSource.GetAttribute{T}(), references to all Util.Attributes 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 IncrementToken().

Returns: false for end of stream; true otherwise

virtual void Lucene.Net.Analysis.TokenStream.Reset ( )

virtual

Resets this stream to the beginning. This is an optional operation, so subclasses may or may not implement this method. 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 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 Reset()).

Definition at line 144 of file TokenStream.cs.

The documentation for this class was generated from the following file:

core/Analysis/TokenStream.cs

Public Member Functions

Protected Member Functions

Additional Inherited Members

Detailed Description

Member Function Documentation