Hi Sanne,
This is example code used e.g. in my applications. This method allows you to
create an analyzer via reflection for both cases: default ctor or with version:
final Analyzer createAnalyzer(String className, Version matchVersion) throws
Exception {
final Class<? extends Analyzer> clazz =
Class.forName(className).asSubclass(Analyzer.class);
try {
// first try to use a ctor with version parameter (needed for many new
Analyzers that have no default one anymore
return clazz.getConstructor(Version.class).newInstance(matchVersion);
} catch (NoSuchMethodException nsme) {
// otherwise use default ctor
return clazz.newInstance();
}
}
The method takes a Version parameter, that you should really use (and not
LUCENE_CURRENT!!!). You should add an extra configuration option in your
software for a default version that is used everywhere when you instantiate
lucene objects (like query parser and so on). By this you preserve the
compatibility after upgrades.
Just add a option somewhere in your config files, and assign this to a final
Version constant in your application using Version.valueOf(StringFromFile).
Hope that helps,
Uwe
-----
Uwe Schindler
H.-H.-Meier-Allee 63, D-28213 Bremen
http://www.thetaphi.de
eMail: u...@thetaphi.de
> -----Original Message-----
> From: Uwe Schindler [mailto:u...@thetaphi.de]
> Sent: Sunday, February 07, 2010 6:54 PM
> To: java-dev@lucene.apache.org
> Subject: RE: Having a default constructor in Analyzers
>
> Hi Sanne,
>
> Exactly that usage we want to prevent. Using Version.LUCENE_CURRENT is
> the badest thing you can do if you want to later update your Lucene
> version and do not want to reindex all your indexes (see javadocs).
>
> It is easy to modify your application to create analyzers even from
> config files using the reflection way. Just find a constructor taking
> Version and call newInstance() on it, not directly on the Class. It's
> just one line of code more.
>
> Uwe
>
> -----
> Uwe Schindler
> H.-H.-Meier-Allee 63, D-28213 Bremen
> http://www.thetaphi.de
> eMail: u...@thetaphi.de
>
> > -----Original Message-----
> > From: Sanne Grinovero [mailto:sanne.grinov...@gmail.com]
> > Sent: Sunday, February 07, 2010 6:33 PM
> > To: java-dev@lucene.apache.org
> > Subject: Having a default constructor in Analyzers
> >
> > Hello,
> > I've seen that some core Analyzers are now missing a default
> > constructor; this is preventing many applications to configure/load
> > Analyzers by reflection, which is a common use case to have Analyzers
> > chosen in configuration files.
> >
> > Would it be possible to add, for example, a constructor like
> >
> > public StandardAnalyzer() {
> > this(Version.LUCENE_CURRENT);
> > }
> >
> > ?
> >
> > Of course more advanced use cases would need to pass parameters but
> > please make the advanced usage optional; I have now seen more than a
> > single project break because of this (and revert to older Lucene).
> >
> > Regards,
> > Sanne
> >
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>
>
>
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