org.apache.lucene.analysis
Class TokenStream

java.lang.Object
  org.apache.lucene.analysis.TokenStream

Direct Known Subclasses:

EmptyTokenStream, PrefixAndSuffixAwareTokenFilter, PrefixAwareTokenFilter, ShingleMatrixFilter, SingleTokenTokenStream, TokenFilter, Tokenizer

public abstract class TokenStream
extends Object

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.

NOTE: subclasses must override next(Token). It's also OK to instead override next() but that method is now deprecated in favor of next(Token).

Constructor Summary

TokenStream()

Method Summary

void	close() Releases resources associated with this stream.
Token	next() Deprecated. The returned Token is a "full private copy" (not re-used across calls to next()) but will be slower than calling next(Token) instead..
Token	next(Token reusableToken) Returns the next token in the stream, or null at EOS.
void	reset() Resets this stream to the beginning.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TokenStream

public TokenStream()

Method Detail

next

public Token next()
           throws IOException

Deprecated. The returned Token is a "full private copy" (not re-used across calls to next()) but will be slower than calling next(Token) instead..

Returns the next token in the stream, or null at EOS.

Throws:

IOException

next

public Token next(Token reusableToken)
           throws IOException

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):

• A consumer must fully consume the previously returned Token before calling this method again.
• A producer must call Token.clear() before setting the fields in it & returning it

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.

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

reset

public void reset()
           throws IOException

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()).

Throws:

IOException

close

public void close()
           throws IOException

Releases resources associated with this stream.

Throws:

IOException