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Re: [Geotools-gt2-users] ClassLoader problems with GeoTools/RCP
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From: Kirby B. <com...@ho...> - 2007-03-20 16:57:29
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All,
Sorry to be slow on responding.
Technically speaking, BuddyLoaders don't all have the same class loader,
it's just that you delegate to your buddy class loaders (in very weird
corner cases the difference is important as I learned the hard way). If you
really need them to be in the same class loader you use fragments.
I have one plug-in that includes the "core" GeoTools plug-ins:
geoapi-2.0.jar
jsr108-0.01.jar
gt2-api-2.2.1.jar
gt2-main-2.2.1.jar
gt2-referencing-2.2.1.jar
That plug-in depends upon two other plug-ins that include vecmath and JAI.
Inside of the core plugin's MANIFEST.MF include a line like this:
Eclipse-BuddyPolicy: registered
Then inside of an extension of that plug-in use:
Eclipse-RegisterBuddy: ${CORE_PLUGIN_ID}
At that point, everything has just worked for me. I have managed to put all
of the dependencies of GeoTools into an RCP plug-ins (including JAI) and can
run off a freshly installed JRE. BuddyLoading breaks certain assumptions in
the ClassLoader, which can lead to deadlock. I've never had it happen with
GeoTools, but have in other code bases. Using Fragments would solve that
problem.
The other alternative is to have a core plug-in and fragments. The
Fragments would cause them to all be in the same class loader.
Is there any interest in writing "OSGi" compliant or friendly bundles? You
wouldn't have to change the factory at interfaces at all. I've written
Factory classes that move between Eclipse plug-ins and straight JRE
classloaders without issue. While, OSGi while might be EVIL if your
methodology doesn't account for them, are a godsend in large scale
applications with numerous dependencies that have conflicting versions.
Just dumping everything onto a single classpath can be far more problematic
when integrating numerous disparate libraries.
I don't think that it'd be a huge deal to write a translator that tranformed
configuration from one format into the other, so you only have to maintain
one copy of the config and run a tool at build time. I've made GeoTools
work in Eclipse RCP bundles (using extension points, I haven't done it on
raw OSGi Bundles w/ Services) with everything being packaged in a way that
you can pull just the pieces you need.
I have made a factory pattern that works inside and out of an Eclipse RCP
classloader environment. I just have an extension point that is the
interface name, and then register all implementations with the concrete
class name as the key. When doing constructing one, pull the extensions one
of the attributes will be the plug-in name. The plug-in name is a key you
can use to pull the classloader that will allow you to do Class clazz =
ClassLoader.resolveClass(...); I don't believe it matters if you export
that class at that point, because you are using the classloader that knows
about it.
Proceed with normal reflection at this point. If there is interest, I'd be
absolutely thrilled to help get GeoTools to be Eclipse Plug-in friendly or
OSGi bundle complaint. It'd save me a great deal of parallel effort.
Kirby
>From: Jody Garnett <jga...@re...>
>To: Justin Deoliveira <jde...@op...>
>CC: Martin Desruisseaux <mar...@ge...>,Gary Lucas
><gw...@so...>,geo...@li...
>Subject: Re: [Geotools-gt2-users] ClassLoader problems with GeoTools/RCP
>Date: Fri, 16 Mar 2007 10:24:31 -0700
>
>Justin is correct - the GeoTools "lookup and intergration" code is broken.
>
>Indeed I am talking with Martin right now about a couple proposed fixes :-(
>
>For now you are stuck dumping eveything into a single plugin (or many
>buddy plugins) so they
>all get in the same class loader.
>
>At a technical level our "Factory Lookup" is done in the same manner as
>ImageIO ... it goes into
>each jar looking for a directory "META-INF/services/" where have a file
>named after the interface
>being discovered. The file lists all the instances that the jar provides.
>
>The OSGi classloader is EVIL and locks down the packages that can be
>loaded by dependent
>plugins (they chain class loaders so a dependent plugin is loaded using
>a child classloader). However
>you have to list manually the packages that are visible - and they don't
>let you list "META-INF/services/"
>(as it is not a valid package name). So the that file is not available
>as a resource :-(
>
>The proposed solution is to register a FactoryIterator with GeoTools;
>and then implement one
>that plugin extension point (so yes we will need to duplicate all the
>information contained in META-INF/services).
>
>Cheers,
>Jody
>
>Justin Deoliveira wrote:
> > Hi Gary,
> >
> > Yes the breakdown geotools modules wont map cleanly to eclipse rcp
> > plugins due to class loading issues. I believe there is some magic you
> > can pull off with "buddy classloading" but I have never tried it out.
> > The udig guys can comment on that.
> >
> > The udig approach is to have a single "libs" plugin which essentially
> > contains the entire geotools library in one plugin. What is your plugin
> > structure?
> >
> > -Justin
> >
> > Gary Lucas wrote:
> >
> >> I am attempting to use GeoTools to create and eclipse plug-in that
>draws
> >> maps. I've had some luck writing conventional Java applications and
> >> decided to move forward a Rich Client Platform (RCP) implementation to
> >> take advantage of the better GUI support. Anyway, I've hit a roadblock.
> >>
> >> At the point in the program execution when I try to create my first
>map,
> >> the program fails when calling a constructor for a class. The class
> >> loads a shape file and creates a map context. A key point here is that
> >> the constructor itself is empty (it's just a stub for now) and the
> >> method that creates the map context is NEVER called. Even so, if the
> >> statement
> >>
> >> MapContext mapContext = DefaultMapContext();
> >>
> >> is called, the program fails. If the line is commented out, it
>continues
> >> on... though of course there's little point in doing so since it will
> >> never be able to render a map. A similar thing happens if I use
> >> DefaultMapLayer. Interestingly enough, the program is able to include
> >> code open a shape file and create a ShapeFileDatastore.
> >>
> >> Clearly the problem has to do with the ClassLoader and Eclipse's notion
> >> of installing custom class loaders. I am new to the RCP and plug-ins,
> >> so I don't really know how to proceed from here.
> >>
> >> I was wondering whether anyone had a solution for this problem. I know
> >> that the uDig folks must have worked it out, but I haven't found any
> >> relevant discussion in the archives for this mailing list.
> >>
> >> As I have said so many times before on this discussion group: thanks in
> >> advance for your help.
> >>
> >> Gary
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> ---
> >> Gary W. Lucas, Senior Software Engineer
> >> Sonalysts, Inc
> >> 215 Parkway North
> >> Waterford, CT 06320
> >> (860) 326-3682
> >>
> >>
> >>
> >> !DSPAM:4007,45fa8ed8230332051017194!
> >>
> >>
> >>
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