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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-1448) add getFinalOffset() to TokenStream
Date Mon, 01 Dec 2008 13:42:44 GMT


Michael McCandless commented on LUCENE-1448:

I'm torn on how to add getFinalOffset()/getFinalPositionIncrement().

One option is to add a set/getFinalOffset to OffsetAttribute.  The
downside here is it's another int added to that class, that gets
copied for caching streams yet is only used at the very end.

Another option is to "define" the API such that when incrementToken()
returns false, then it has actually advanced to an "end-of-stream
token".  OffsetAttribute.getEndOffset() should return the final
offset.  Since we have not released the new API, we could simply make
this change (and fix all instances in the core/contrib that use the
new API accordingly).  I think I like this option best.

Yet another option is to open up "per stream" attrs rather than "per
token attrs".  This seems like alot of added complexity.  Are there
other things, besides these two, that would be an example of a "per
stream" attr?

> add getFinalOffset() to TokenStream
> -----------------------------------
>                 Key: LUCENE-1448
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Analysis
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.9
>         Attachments: LUCENE-1448.patch, LUCENE-1448.patch, LUCENE-1448.patch, LUCENE-1448.patch
> If you add multiple Fieldable instances for the same field name to a document, and you
then index those fields with TermVectors storing offsets, it's very likely the offsets for
all but the first field instance will be wrong.
> This is because IndexWriter under the hood adds a cumulative base to the offsets of each
field instance, where that base is 1 + the endOffset of the last token it saw when analyzing
that field.
> But this logic is overly simplistic.  For example, if the WhitespaceAnalyzer is being
used, and the text being analyzed ended in 3 whitespace characters, then that information
is lost and then next field's offsets are then all 3 too small.  Similarly, if a StopFilter
appears in the chain, and the last N tokens were stop words, then the base will be 1 + the
endOffset of the last non-stopword token.
> To fix this, I'd like to add a new getFinalOffset() to TokenStream.  I'm thinking by
default it returns -1, which means "I don't know so you figure it out", meaning we fallback
to the faulty logic we have today.
> This has come up several times on the user's list.

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