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
ATokenStreamenumerates the sequence of tokens, either fromFields of aDocumentor from query text.This is an abstract class; concrete subclasses are:
Tokenizer, aTokenStreamwhose input is a Reader; andTokenFilter, aTokenStreamwhose input is anotherTokenStream.
TokenStreamextendsAttributeSource, which provides access to all of the tokenAttributes for theTokenStream. Note that only one instance perAttributeImplis created and reused for every token. This approach reduces object creation and allows local caching of references to theAttributeImpls. SeeincrementToken()for further details.The workflow of the new
TokenStreamAPI is as follows:- Instantiation of
TokenStream/TokenFilters 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 AttributeFactoryDEFAULT_TOKEN_ATTRIBUTE_FACTORYDefaultAttributeFactoryinstance that should be used for TokenStreams.
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Constructor Summary
Constructors Modifier Constructor Description protectedTokenStream()A TokenStream using the default attribute factory.protectedTokenStream(AttributeFactory factory)A TokenStream using the supplied AttributeFactory for creating newAttributeinstances.protectedTokenStream(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 voidclose()Releases resources associated with this stream.voidend()This method is called by the consumer after the last token has been consumed, afterincrementToken()returnedfalse(using the newTokenStreamAPI).abstract booleanincrementToken()Consumers (i.e.,IndexWriter) use this method to advance the stream to the next token.voidreset()This method is called by a consumer before it begins consumption usingincrementToken().-
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
DefaultAttributeFactoryinstance 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 newAttributeinstances.
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Method Detail
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incrementToken
public abstract boolean incrementToken() throws IOExceptionConsumers (i.e.,IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriateAttributeImpls 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 allAttributeImpls 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 IOExceptionThis method is called by the consumer after the last token has been consumed, afterincrementToken()returnedfalse(using the newTokenStreamAPI). 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 IOExceptionThis 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.,Tokenizerwill throwIllegalStateExceptionon further usage).- Throws:
IOException
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close
public void close() throws IOExceptionReleases 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.,Tokenizerwill throwIllegalStateExceptionon reuse).- Specified by:
closein interfaceAutoCloseable- Specified by:
closein interfaceCloseable- Throws:
IOException
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