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https://issues.apache.org/jira/browse/LUCENE-8651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16752080#comment-16752080
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Alan Woodward commented on LUCENE-8651:
---------------------------------------
It's an interesting question. Tokenizers generally should only be instantiated
as part of Analyzer.createComponents(), as that's where things like setReader()
are handled - a consumer of a TokenStream shouldn't need to worry about that at
all. I think some clarifying documentation on Tokenizer is a good idea -
please feel free to put up a patch!
> Tokenizer implementations can't be reset
> ----------------------------------------
>
> Key: LUCENE-8651
> URL: https://issues.apache.org/jira/browse/LUCENE-8651
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/analysis
> Reporter: Dan Meehl
> Priority: Major
> Attachments: LUCENE-8650-2.patch, LUCENE-8651.patch, LUCENE-8651.patch
>
>
> The fine print here is that they can't be reset without calling setReader()
> every time before reset() is called. The reason for this is that Tokenizer
> violates the contract put forth by TokenStream.reset() which is the following:
> "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."
> Tokenizer implementation's reset function can't reset in that manner because
> their Tokenizer.close() removes the reference to the underlying Reader
> because of LUCENE-2387. The catch-22 here is that we don't want to
> unnecessarily keep around a Reader (memory leak) but we would like to be able
> to reset() if necessary.
> The patches include an integration test that attempts to use a
> ConcatenatingTokenStream to join an input TokenStream with a KeywordTokenizer
> TokenStream. This test fails with an IllegalStateException thrown by
> Tokenizer.ILLEGAL_STATE_READER.
>
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