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https://issues.apache.org/jira/browse/LUCENE-2915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12993080#comment-12993080
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Uwe Schindler edited comment on LUCENE-2915 at 2/10/11 3:06 PM:
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Hi Mike,
I would prefer to remove the hardcoded core providers from source code. In Java
is a standard mechanism (so called Service Provider framework) that can be used
to find out all codecs that ship with all given JAR files in classpath. This
makes it easy to add custom codecs, you just add the JAR file to class path and
it is available.
If you like I could code the lookup code (unfortunately its only "standardized"
in Java 6, but its available in a different public class since Java 1.2. It is
mainly used by:
- XML, XSLT (all of javax.xml)
- image formats (png, gif,..)
- ...
In general it works very simple:
The JAR file contains a MANIFEST that lists all classes that implement a codec
under a key that is the class name of the abstract base class. A simple example
is: if you plug xercesImpl.jar into your classpath, it's manifest contains a
javax.xml.dom.DocumentBuilder=someClass. Based on this information
DocumentuilderFactory returns a suitable implementation of a DOM parser. The
same would be for Lucene, the MANIFEST of lucene-core.jar would contain a
simple list of classes (all of them are returned to the provider!). If you then
add the JAR file of contrib-misc to it, also the AppendingOnlyCoded would
automatically be available.
Implementation is quite simple: you can ask the service provider API for the
above key (in our case a oal.index.Codec-like one) and the codec provier
returns an Iterator of implementation classes. Those would get registered on
Startup of DefaultCodecProvider.
was (Author: thetaphi):
Hi Mike,
I would prefer to remove the hardcoded core providers from source code. In Java
is a standard mechanism (so called Service Provider framework) that can be used
to find out all codecs that ship with all given JAR files in classpath. This
makes it easy to add custom codecs, you just add the JAR file to class path and
it is available.
If you like I could code the lookup code (unfortunately its only "standardized"
in Java 6, but its available in a different public class since Java 1.2. It is
mainly used by:
- XML, XSLT (all of javax.xml)
- image formats (png, gif,..)
-
In general it works very simple:
The JAR file contains a MANIFEST that lists all classes that implement a codec
under a key that is the class name of the abstract base class. A simple example
is: if you plug xercesImpl.jar into your classpath, it's manifest contains a
javax.xml.dom.DocumentBuilder=someClass. Based on this information
DocumentuilderFactory returns a suitable implementation of a DOM parser. The
same would be for Lucene, the MANIFEST of lucene-core.jar would contain a
simplar list of classes (all are returned to the provider!). If you then add
the JAR file of contrib-misc to it, also the AppendingOnlyCoded would also be
available.
Implementation is quite simple: you can ask the service provider API for the
above key (in our case a oal.index.Codec-like one) and the codec provier
returns an Iterator of implementation classes. Those would get registered on
Startup of DefaultCodecProvider.
> make CoreCodecProvider convenience class so apps can easily pick per-field
> codecs
> ---------------------------------------------------------------------------------
>
> Key: LUCENE-2915
> URL: https://issues.apache.org/jira/browse/LUCENE-2915
> Project: Lucene - Java
> Issue Type: Improvement
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Fix For: 4.0
>
> Attachments: LUCENE-2915.patch
>
>
> We already have DefaultCodecProvider, which simply registers all core codecs
> and uses Standard for all fields, but it's package private.
> We should make this public, and name it CoreCodecProvider.
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