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Re: [equinox-dev] Bridging the plain Java and OSGi classloading worlds
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If the service defined and registered inside the OSGi framework is
relatively simple, you might consider proxying your requests using
Java reflection.
For example, if you've launched the OSGi framework using the new
standard launch APIs, you will have access to the framework's bundle
context, through which you can query the service. It will be returned
as an object. If you know the expected signatures of the service
methods, you can query its methods and invoke them without having code
statically linked to it (which won't work because that service comes
from a class loader inside OSGi). Reflection in effect bypasses the
class loader.
I've done this myself for some simple cases, and the disclaimer is
around the "relatively simple." If your service uses only JDK classes,
this is pretty easy. It gets really messy really fast when you find
yourself proxying multiple calls and queries.
In my case I queried the package admin service and refreshed packages,
all without compiling against the PackageAdmin service class in my
code. As a matter of fact, this was before the new OSGi framework
launch API, and I created a URLClassLoader for the Equinox bundle, and
instantiated and invoking the EclipseStarter from the outside. In
other words, my code didn't even have access to org.osgi.framework.*...
I hope this sketch gives you some ideas.
/djk
On Aug 19, 2009, at 1:32 PM, Michael Furtak wrote:
Hi Hal,
Thanks for those references. They were helpful. It feels like I’m
close, but problems remain.
Also, I’m a bit confused as to whether the noted techniques can help
my problem. My understanding of the system packages and boot
delegation stuff is that it helps OSGi find classes that are not
explicitly exported from any of the OSGi bundles (i.e. java.*,
javax.* stuff, etc.)
My dilemma is somewhat the opposite. I’m originating from Java,
outside of the OSGi environment, but want to call objects created
inside of OSGi. Of course, this leads to a ClassCastException when I
get the service object and try to refer to it by its interface as
loaded in Java land.
I’ve attached my source w/ some class/package names changed to
protect the innocent. Also attached is my config.ini file. Without
the org.osgi.framework.system.packages.extra directive, the
ClassCastException occurs. With it, I don’t get a callback on my
ServiceTrackerCustomizer’s addedService() method.
Do you have any further thoughts?
Thanks in advance,
-Mike
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From: equinox-dev-bounces@xxxxxxxxxxx [mailto:equinox-dev-bounces@xxxxxxxxxxx
] On Behalf Of Hal Hildebrand
Sent: Wednesday, August 19, 2009 3:18 PM
To: Equinox development mailing list
Subject: Re: [equinox-dev] Bridging the plain Java and OSGi
classloading worlds
You can also check out: http://felix.apache.org/site/apache-felix-framework-launching-and-embedding.html
note the section "Creating and Configuring the Framework Instance",
and the use of the property
"org.osgi.framework.system.packages.extra" which makes this a bit
easier. Works the same way with Equinox.
On Aug 19, 2009, at 12:13 PM, Hal Hildebrand wrote:
Sure. See http://blog.springsource.com/2009/01/19/exposing-the-boot-classpath-in-osgi/
for an in depth discussion by Costin of SS.
On Aug 19, 2009, at 12:08 PM, Michael Furtak wrote:
Hi Hal,
Thanks very much for your reply. I’m heartened that you’re confident
in this possibility. Is there any documentation for the option you
mention that I can refer to?
Thanks,
-Mike
THIS MESSAGE IS INTENDED FOR THE USE OF THE PERSON TO WHOM IT IS
ADDRESSED. IT MAY CONTAIN INFORMATION THAT IS PRIVILEGED,
CONFIDENTIAL AND EXEMPT FROM DISCLOSURE UNDER APPLICABLE LAW. If you
are not the intended recipient, your use of this message for any
purpose is strictly prohibited. If you have received this
communication in error, please delete the message and notify the
sender so that we may correct our records.
From: equinox-dev-bounces@xxxxxxxxxxx [mailto:equinox-dev-bounces@xxxxxxxxxxx
] On Behalf Of Hal Hildebrand
Sent: Wednesday, August 19, 2009 3:01 PM
To: Equinox development mailing list
Subject: Re: [equinox-dev] Bridging the plain Java and OSGi
classloading worlds
sure, you just have to have a class loader in common. The way this
would work is to modify the exports of the System bundle (an option
when starting the framework in Equinox) to export the classes from
the base class path you need. Then there is no class loader issues,
as they're both using the same.
On Aug 19, 2009, at 11:56 AM, Michael Furtak wrote:
Hi all,
I am using the EclipseStarter.startup(…) method to bring up the
Equninox framework from within a plain ol’ Java application. My
question is this:
Is it possible to allow the plain ol’ Java environment to get and
call service objects from the OSGi side? I know their respective
classloader environments are disjoint, but is there any hope at all
of bridging them? Has anyone been dumb/crazy enough to want to do
this?
Thanks,
-Mike
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are not the intended recipient, your use of this message for any
purpose is strictly prohibited. If you have received this
communication in error, please delete the message and notify the
sender so that we may correct our records.
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<JavaOsgiBootstrapper.java><config.ini>
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