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=10076)
- 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: [email protected]
> -----Original Message-----
> From: VIGNESH S [mailto:[email protected]]
> Sent: Saturday, July 13, 2013 5:52 PM
> To: [email protected]
> Subject: Re: A SPI class of type org.apache.lucene.codecs.Codec with name
> 'Lucene42' does not exist
>
> Hi Robert,
>
> Thanks for your reply.
>
> If possible,can you please explain why this new class loading mechanism was
> introduced in Lucene 4
>
> Thanks and Regards
> Vignesh
>
>
> On Sat, Jul 13, 2013 at 6:56 PM, Robert Muir <[email protected]> wrote:
>
> > 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 <[email protected]>
> > 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 <[email protected]>
> > wrote:
> > >
> > > > On Sat, Jul 13, 2013 at 10:25 AM, VIGNESH S
> > > > <[email protected]>
> > > > 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
> > >
> >
>
>
>
> --
> Thanks and Regards
> Vignesh Srinivasan
> 9739135640
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