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From: "Uwe Schindler" <uwe@thetaphi.de>
To: <java-user@lucene.apache.org>
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Subject: RE: A SPI class of type org.apache.lucene.codecs.Codec with name
 'Lucene42' does not exist
Date: Sat, 13 Jul 2013 23:57:31 +0200
Message-ID: <003001ce8013$f98dd940$eca98bc0$@thetaphi.de>
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Hi Vignesh,

Lucene 4 supports now so called "Codecs" which are implementation =
classes for custom index encodings. E.g. you can exchange the default =
postings list by a custom format. Those implementations are classes that =
extend an abstract base class/interface to implement this functionality. =
To plug this into the Lucene index format, IndexReader and IndexWriter =
need the knowledge, which codec type was used to load the correct =
classes. This is done by the Java Service Provider interface (SPI), =
which is used quite often e.g. to load custom image formats, XML =
parsers, Charsets,... in the JDK. The codec implementation classes are =
listed in the JAR files META-INF section and then loaded by the code and =
register themselves through the codec manager. There is no custom class =
loading involved, it's all just plain Java. E.g. =
Charset.forName("ISO-8859-1") in the JDK does exactly the same: It scans =
META-INF for Charset files, loads all charsets and looks them up by =
name. You can use this to e.g. plug in ICU4J to have more charsets than =
in the default JDK.

In your case there might be several reasons for this to fail:
- Android only packs directly referenced classes into the DEX file =
(similar to the Maven Shade plugin or the Jarjar tool). The codec =
classes are not referenced my any internal Lucene class (only loaded via =
SPI) so it might happen that the DEX tool was missing to pack them into =
the resulting package.
- You must append all META-INF files with the same name (if you merge =
multiple Lucene JARS with different codecs). The Maven shade plugin can =
do this for you.
- Android's functionality behind ClassLoader#findResources() may be =
broken (which is used to list the META-INF files, e.g. see =
https://code.google.com/p/android/issues/detail?id=3D10076)
- Be sure that the META-INF directory is in the root of your classes =
folder (resp. DEX file). Apkbuilder by default does not add resources!

I know form other developers that they definitely got Lucene 4 running =
with Android, but the Lucene team can give no support, because it's an =
unsupported configuration.

Uwe

-----
Uwe Schindler
H.-H.-Meier-Allee 63, D-28213 Bremen
http://www.thetaphi.de
eMail: uwe@thetaphi.de

> -----Original Message-----
> From: VIGNESH S [mailto:vigneshklncit@gmail.com]
> Sent: Saturday, July 13, 2013 5:52 PM
> To: java-user@lucene.apache.org
> Subject: Re: A SPI class of type org.apache.lucene.codecs.Codec with =
name
> 'Lucene42' does not exist
>=20
> Hi Robert,
>=20
> Thanks for your reply.
>=20
> If possible,can you please explain why this new class loading =
mechanism was
> introduced in Lucene 4
>=20
> Thanks and Regards
> Vignesh
>=20
>=20
> On Sat, Jul 13, 2013 at 6:56 PM, Robert Muir <rcmuir@gmail.com> wrote:
>=20
> > Open a bug with android team... the problem is android isn't java =
(and
> > doesnt implement/follow the spec)
> >
> > On Sat, Jul 13, 2013 at 4:31 AM, VIGNESH S <vigneshklncit@gmail.com>
> > wrote:
> >
> > > Hi,
> > >
> > > I did not striped META-INF/services and it contains the files.
> > >
> > > Even when i combined with other jars,i manually appended those
> > > entries in Meta-inf/services..
> > >
> > > The problem has some thing to do with the way android loads =
classes.
> > >
> > > any comments welcome.
> > >
> > >
> > > Thanks adnd Regards
> > > Vignesh
> > >
> > >
> > > On Sat, Jul 13, 2013 at 1:57 PM, Thomas Matthijs =
<lists@selckin.be>
> > wrote:
> > >
> > > > On Sat, Jul 13, 2013 at 10:25 AM, VIGNESH S
> > > > <vigneshklncit@gmail.com>
> > > > wrote:
> > > >
> > > > > Hi,
> > > > >
> > > > > I tried indexing in Desktop..It works fine.
> > > > > The above error loading error comes only in android..
> > > > > Any comments..
> > > >
> > > >
> > > > Don't strip META-INF/services files out of the jars
> > > >
> > >
> > >
> > >
> > > --
> > > Thanks and Regards
> > > Vignesh Srinivasan
> > > 9739135640
> > >
> >
>=20
>=20
>=20
> --
> Thanks and Regards
> Vignesh Srinivasan
> 9739135640


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