org.apache.lucene.analysis
Class CachingTokenFilter

java.lang.Object
  extended by org.apache.lucene.util.AttributeSource
      extended by org.apache.lucene.analysis.TokenStream
          extended by org.apache.lucene.analysis.TokenFilter
              extended by org.apache.lucene.analysis.CachingTokenFilter

public class CachingTokenFilter
extends TokenFilter

This class can be used if the token attributes of a TokenStream are intended to be consumed more than once. It caches all token attribute states locally in a List.

CachingTokenFilter implements the optional method TokenStream.reset(), which repositions the stream to the first Token.


Nested Class Summary
 
Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
AttributeSource.AttributeFactory, AttributeSource.State
 
Field Summary
 
Fields inherited from class org.apache.lucene.analysis.TokenFilter
input
 
Constructor Summary
CachingTokenFilter(TokenStream input)
           
 
Method Summary
 void end()
          Performs end-of-stream operations, if any, and calls then end() on the input TokenStream.

NOTE: Be sure to call super.end() first when overriding this method.

 boolean incrementToken()
          Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.
 Token next()
          Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.
 Token next(Token reusableToken)
          Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.
 void reset()
          Reset the filter as well as the input TokenStream.
 
Methods inherited from class org.apache.lucene.analysis.TokenFilter
close
 
Methods inherited from class org.apache.lucene.analysis.TokenStream
getOnlyUseNewAPI, setOnlyUseNewAPI
 
Methods inherited from class org.apache.lucene.util.AttributeSource
addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, restoreState, toString
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

CachingTokenFilter

public CachingTokenFilter(TokenStream input)
Method Detail

next

public final Token next(Token reusableToken)
                 throws IOException
Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.

Description copied from class: TokenStream
Returns the next token in the stream, or null at EOS. When possible, the input Token should be used as the returned Token (this gives fastest tokenization performance), but this is not required and a new Token may be returned. Callers may re-use a single Token instance for successive calls to this method.

This implicitly defines a "contract" between consumers (callers of this method) and producers (implementations of this method that are the source for tokens):

Also, the producer must make no assumptions about a Token after it has been returned: the caller may arbitrarily change it. If the producer needs to hold onto the Token for subsequent calls, it must clone() it before storing it. Note that a TokenFilter is considered a consumer.

Overrides:
next in class TokenStream
Parameters:
reusableToken - a Token that may or may not be used to return; this parameter should never be null (the callee is not required to check for null before using it, but it is a good idea to assert that it is not null.)
Returns:
next Token in the stream or null if end-of-stream was hit
Throws:
IOException

next

public final Token next()
                 throws IOException
Deprecated. Will be removed in Lucene 3.0. This method is final, as it should not be overridden. Delegates to the backwards compatibility layer.

Description copied from class: TokenStream
Returns the next Token in the stream, or null at EOS.

Overrides:
next in class TokenStream
Throws:
IOException

incrementToken

public final 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) or downcasts, 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().

Overrides:
incrementToken in class TokenStream
Returns:
false for end of stream; true otherwise

Note that this method will be defined abstract in Lucene 3.0.

Throws:
IOException

end

public final void end()
               throws IOException
Description copied from class: TokenFilter
Performs end-of-stream operations, if any, and calls then end() on the input TokenStream.

NOTE: Be sure to call super.end() first when overriding this method.

Overrides:
end in class TokenFilter
Throws:
IOException

reset

public void reset()
           throws IOException
Description copied from class: TokenFilter
Reset the filter as well as the input TokenStream.

Overrides:
reset in class TokenFilter
Throws:
IOException


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