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From Simon Pepping <spepp...@leverkruid.eu>
Subject Re: Running XML Graphics products on OSGi
Date Tue, 03 Nov 2009 20:51:53 GMT
On Tue, Nov 03, 2009 at 05:18:05PM +0100, Jeremias Maerki wrote:
> Over the past few months, I've started to get FOP, Batik and Commons
> running in an OSGi environment. The first easy step is to just add the
> necessary metadata to the manifest. However, that is not enough in the
> case here. The problem: we're using the JAR Service Provider mechanism
> from the JAR specification (META-INF/services directory in the JARs).
> 
> OSGi doesn't have a hierarchical class loader setup like traditional
> Java applications which is why FOP, for example, may not see all
> available plug-ins anymore if they are not compiled together into a
> monster-JAR.
> 
> The solution was to build an abstraction layer above the direct access
> to the META-INF/services files. In an OSGi-environment, a special
> component (a so-called extender) will watch all available bundles (=JARs)
> in the application. If it finds plug-ins it make them available despite
> the class loader isolation. Well, that's simply the executive summary.
> In the end, this is a replacement for the "Services" class in XML
> Graphics Commons which we use today.

I am surprised that such a utility does not yet exist. Surely FOP is
not the only application that loads plug-ins. Eclipse is based on
plug-ins, but I suppose they solve the problem because you have to
install eclips plug-ins in known places.

Simon

-- 
Simon Pepping
home page: http://www.leverkruid.eu

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