Class TokenStream
- java.lang.Object
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- org.apache.lucene.util.AttributeSource
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- org.apache.lucene.analysis.TokenStream
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- All Implemented Interfaces:
Closeable
,AutoCloseable
- Direct Known Subclasses:
TokenFilter
,Tokenizer
public abstract class TokenStream extends AttributeSource implements Closeable
ATokenStream
enumerates the sequence of tokens, either fromField
s of aDocument
or from query text.This is an abstract class; concrete subclasses are:
Tokenizer
, aTokenStream
whose input is a Reader; andTokenFilter
, aTokenStream
whose input is anotherTokenStream
.
TokenStream
extendsAttributeSource
, which provides access to all of the tokenAttribute
s for theTokenStream
. Note that only one instance perAttributeImpl
is created and reused for every token. This approach reduces object creation and allows local caching of references to theAttributeImpl
s. SeeincrementToken()
for further details.The workflow of the new
TokenStream
API is as follows:- Instantiation of
TokenStream
/TokenFilter
s which add/get attributes to/from theAttributeSource
. - The consumer calls
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 consuming 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 theTokenStream
.
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 (seeCachingTokenFilter
, TeeSinkTokenFilter). For this usecaseAttributeSource.captureState()
andAttributeSource.restoreState(org.apache.lucene.util.AttributeSource.State)
can be used.The
TokenStream
-API in Lucene is based on the decorator pattern. Therefore all non-abstract subclasses must be final or have at least a final implementation ofincrementToken()
! This is checked when Java assertions are enabled.
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Nested Class Summary
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Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
AttributeSource.State
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Field Summary
Fields Modifier and Type Field Description static AttributeFactory
DEFAULT_TOKEN_ATTRIBUTE_FACTORY
DefaultAttributeFactory
instance that should be used for TokenStreams.
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Constructor Summary
Constructors Modifier Constructor Description protected
TokenStream()
A TokenStream using the default attribute factory.protected
TokenStream(AttributeFactory factory)
A TokenStream using the supplied AttributeFactory for creating newAttribute
instances.protected
TokenStream(AttributeSource input)
A TokenStream that uses the same attributes as the supplied one.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description void
close()
Releases resources associated with this stream.void
end()
This method is called by the consumer after the last token has been consumed, afterincrementToken()
returnedfalse
(using the newTokenStream
API).abstract 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 usingincrementToken()
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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
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Field Detail
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DEFAULT_TOKEN_ATTRIBUTE_FACTORY
public static final AttributeFactory DEFAULT_TOKEN_ATTRIBUTE_FACTORY
DefaultAttributeFactory
instance that should be used for TokenStreams.
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Constructor Detail
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TokenStream
protected TokenStream()
A TokenStream using the default attribute factory.
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TokenStream
protected TokenStream(AttributeSource input)
A TokenStream that uses the same attributes as the supplied one.
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TokenStream
protected TokenStream(AttributeFactory factory)
A TokenStream using the supplied AttributeFactory for creating newAttribute
instances.
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Method Detail
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incrementToken
public abstract boolean incrementToken() throws IOException
Consumers (i.e.,IndexWriter
) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriateAttributeImpl
s 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)
andAttributeSource.getAttribute(Class)
, references to allAttributeImpl
s 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
- Throws:
IOException
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end
public void end() throws IOException
This method is called by the consumer after the last token has been consumed, afterincrementToken()
returnedfalse
(using the newTokenStream
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.
Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.
If you override this method, always call
super.end()
.- Throws:
IOException
- If an I/O error occurs
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reset
public void reset() throws IOException
This method is called by a consumer before it begins consumption usingincrementToken()
.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 throwIllegalStateException
on further usage).- Throws:
IOException
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close
public void close() throws IOException
Releases resources associated with this stream.If you override this method, always call
super.close()
, otherwise some internal state will not be correctly reset (e.g.,Tokenizer
will throwIllegalStateException
on reuse).- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Throws:
IOException
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