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RE: [equinox-dev] Bridging the plain Java and OSGi classloading worlds

Aha! The remaining key was removing the OSGi bundle that contained my service interface, and as you said, forcing OSGi to load them from the parent environment. I now have a successful service object invocation from outside to within!

 

 

For anyone else that might want to try this, it is good to know that the org.osgi.framework.system.packages.extra property accepts version statements like a normal manifest import/export:

 

com.cra.myservice;version="1.0.0",com.cra.myservice.xml;version="1.0.0"

 

I’m sure this is not news to you, but it was a nice discovery for me!

 

 

Thank you for your patient explanation and guidance.

-Mike Furtak

 

 
 
 
 
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From: equinox-dev-bounces@xxxxxxxxxxx [mailto:equinox-dev-bounces@xxxxxxxxxxx] On Behalf Of Hal Hildebrand
Sent: Wednesday, August 19, 2009 6:24 PM
To: Equinox development mailing list
Subject: Re: [equinox-dev] Bridging the plain Java and OSGi classloading worlds

 

Okay, I'll go into a bit more detail.

 

At the base of the problem, the issue is that you have to have a common class loader between the two environments.  Inside the OSGi environment, this is accomplished in only one of two ways:

 

  1. Boot class path
  2. System Bundle

 

A third mechanism, detailed by Costin in the SS post I provided earlier, uses fragments of the System bundle, which amounts to #2.

 

Consequently, the classes you want to share between the environment outside of OSGi, and within the OSGi container MUST originate from outside the OSGi container.  What this means is that you cannot provide an OSGi bundle containing these classes, load them into the OSGi container, and expect them to be visible from outside the OSGi container.  The equivalent, in JEE land, would be to expect a Servlet class loaded from within a WAR context to be visible in another JEE application scope - it just doesn't work and without bending both time in space in ways that even Cthulu would find a crime, essentially impossible.

 

In essence, this means that unless you're using the System bundle fragments facade that Costin outlines, you won't be loading these shared classes by loading them with OSGi bundles.

 

I would also suggest that you use the new OSGi standard for launching frameworks, defined in RFC 132.  You can find the doc in the 4.2 spec: <http://www.osgi.org/download/r4-v4.2-core-draft-20090310.pdf> - section 4.2.1.  Far cleaner and simpler.

 

 

 

 

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

 

 

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

 

 

 

 

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.

 

 

 

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<JavaOsgiBootstrapper.java><config.ini>

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