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https://issues.apache.org/jira/browse/LUCENE-3055?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13027179#comment-13027179
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Uwe Schindler commented on LUCENE-3055:
---------------------------------------
{quote}
>From my perspective the most important reason is to avoid a huge performance
>trap: previously if you subclassed one of these analyzers, override
>tokenStream(), and added SpecialFilter for example, most of the time users
>would actually slow down indexing, because now reusableTokenStream() cannot be
>used by the indexer.
{quote}
Additionally, exactly this special case (overwriting one of the methods) was
the biggest problem, leading to ugly reflection based checks in Lucene 3.0: In
3.0 StandardAnalyzer correctly implemented both tokenStream() and
reuseableTokenStream(). As soon as one subclass only overrided tokenStream(),
but the indexer still calling reuseableTokenStream() the changes were not even
used, leading to lots of bug reports. Because of this, a reflection based
backwards hack was done in 3.0 (see o.a.l.util.VirtualMethod class to make this
easier), that prevented the indexer from calling reuseableTokenStream if a
subclass suddenly overwrote only one of the methods. With moving forward in
3.1, these backwards hacks even got heavier (e.g. changes in TokenStreams, new
base class ReuseableAnalyzerBase,...), so the only solution was to enforce the
decorator pattern.
The above example by Robert is the correct way to implement you "factory" of
TokenStreams. Everything else like subclassing StandardAnalyzer is ugly as it
hides what you are really doing. The above pattern does exactly what also
Solr's Schemadoes: You have to explicitely list all your components, making it
clear what your TokenStreams are doing.
Trust me, the above example is shorter than subclassing previous
StandardAnalyzer completely (both tokenStream and reuseableTokenStream) and is
showing like solrschema.xml what your Analyzer looks like (no hidden stuff in
superfactories,...)
> LUCENE-2372, LUCENE-2389 made it impossible to subclass core analyzers
> ----------------------------------------------------------------------
>
> Key: LUCENE-3055
> URL: https://issues.apache.org/jira/browse/LUCENE-3055
> Project: Lucene - Java
> Issue Type: Bug
> Components: Analysis
> Affects Versions: 3.1
> Reporter: Ian Soboroff
>
> LUCENE-2372 and LUCENE-2389 marked all analyzers as final. This makes
> ReusableAnalyzerBase useless, and makes it impossible to subclass e.g.
> StandardAnalyzer to make a small modification e.g. to tokenStream(). These
> issues don't indicate a new method of doing this. The issues don't give a
> reason except for design considerations, which seems a poor reason to make a
> backward-incompatible change
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