Tokenizers (which are the source of Tokens) should call
AttributeSource.clearAttributes() first
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Key: LUCENE-1801
URL: https://issues.apache.org/jira/browse/LUCENE-1801
Project: Lucene - Java
Issue Type: Task
Affects Versions: 2.9
Reporter: Uwe Schindler
Assignee: Uwe Schindler
Fix For: 2.9
This is a followup for LUCENE-1796:
{quote}
Token.clear() used to be called by the consumer... but then it was switched to
the producer here: LUCENE-1101
I don't know if all of the Tokenizers in lucene were ever changed, but in any
case it looks like at least some of these bugs were introduced with the switch
to the attribute API - for example StandardTokenizer did clear it's
reusableToken... and now it doesn't.
{quote}
As alternative to changing all core/contrib Tokenizers to call clearAttributes
first, we could do this in the indexer, what would be a overhead for old token
streams that itsself clear their reusable token. This issue should also update
the Javadocs, to clearly state inside Tokenizer.java, that the source
TokenStream (normally the Tokenizer) should clear *all* Attributes. If it does
not do it and e.g. the positionIncrement is changed to 0 by any TokenFilter,
but the filter does not change it back to 1, the TokenStream would stay with 0.
If the TokenFilter would call PositionIncrementAttribute.clear() (because he is
responsible), it could also break the TokenStream, because clear() is a general
method for the whole attribute instance. If e.g. Token is used as
AttributeImpl, a call to clear() would also clear offsets and termLength, which
is not wanted. So the source of the Tokenization should rest the attributes to
default values.
LUCENE-1796 removed the iterator creation cost, so clearAttributes should run
fast, but is an additional cost during Tokenization, as it was not done
consistently before, so a small speed degradion is caused by this, but has
nothing to do with the new TokenStream API.
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