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Posted to users@felix.apache.org by Roland <wg...@ids.de> on 2013/05/07 17:17:15 UTC
ClassCastException after isAssignableTo()
ClassCastException - not again!
Hello everyone,
after hours of investigation of my problem i resign.
I embedded Apache Felix 4.3 to my host application, i use the maven blugin
to build my project and i have 3 bundles.
Bundle A (systembundle)
Bundle B (exports a interface)
Bundle C (implements this interface)
Bundle C imports the interface and registers the implementation of the
interface as a service.
Bundle A imports the interface and uses this service.
In the activator method of the systembundle (A) i have following code
snippets.
I get a ClassCastException after isAssignableTo().
I checked if the interface and the implementation are fully separated.
The imports and exports of (A,B,C) are correct.
The classloaders are the same, namely the classloader of the bundle which
exports the interface (B).
I checked if the interface-package is imbedded to other bundles, but it
exist only one version in (B).
I checked if i'm inside or outside of OSGi. I'm definitly inside of OSGi.
Have someone an idea whats going wrong? What else can I check?
Maybe a switch to Equinox might help. Should I?
Thank you so much so far.
regards
Roland
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Re: ClassCastException after isAssignableTo()
Posted by Roland <wg...@ids.de>.
appendix...
g! inspect capability service 19 (19 = id of Bundle C)
BundleC [19] provides:
-----------------------------------------------------------------------------------------
service; PackageOfBundleB.IMyService with properties:
service.id = 43
Used by:
org.apache.felix.framework [0]
g! inspect requirement service 0 (0 = id of Systembundle A)
org.apache.felix.framework [0] requires:
----------------------------------------
service; PackageOfBundleB.IMyService provided by:
BundleC [19]
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Re: ClassCastException after isAssignableTo()
Posted by Neil Bartlett <nj...@gmail.com>.
Your code samples have been removed from your email again, and I'm not
sure what else might be missing.
However, I notice one obvious error. The package is exported by Bundle
B, and you are trying to import it in Bundle A and Bundle C....
however, Bundle A is the system bundle. It is impossible for the
system bundle to import packages from ordinary bundles. Instead, you
need to export the package from the system bundle using the
"org.osgi.framework.system.packages.extra" configuration property. At
that going, Bundle B becomes redundant (unless it has other useful
exports).
You could try switching to Equinox; you'll get exactly the same
problem of course :-)
Neil
On Tue, May 7, 2013 at 4:17 PM, Roland <wg...@ids.de> wrote:
> ClassCastException - not again!
>
> Hello everyone,
> after hours of investigation of my problem i resign.
>
> I embedded Apache Felix 4.3 to my host application, i use the maven blugin
> to build my project and i have 3 bundles.
>
> Bundle A (systembundle)
> Bundle B (exports a interface)
> Bundle C (implements this interface)
>
> Bundle C imports the interface and registers the implementation of the
> interface as a service.
> Bundle A imports the interface and uses this service.
>
> In the activator method of the systembundle (A) i have following code
> snippets.
>
>
>
> I get a ClassCastException after isAssignableTo().
>
> I checked if the interface and the implementation are fully separated.
> The imports and exports of (A,B,C) are correct.
> The classloaders are the same, namely the classloader of the bundle which
> exports the interface (B).
> I checked if the interface-package is imbedded to other bundles, but it
> exist only one version in (B).
> I checked if i'm inside or outside of OSGi. I'm definitly inside of OSGi.
>
> Have someone an idea whats going wrong? What else can I check?
> Maybe a switch to Equinox might help. Should I?
>
>
> Thank you so much so far.
> regards
> Roland
>
>
>
> --
> View this message in context: http://apache-felix.18485.x6.nabble.com/ClassCastException-after-isAssignableTo-tp5003252.html
> Sent from the Apache Felix - Users mailing list archive at Nabble.com.
>
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> To unsubscribe, e-mail: users-unsubscribe@felix.apache.org
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Re: ClassCastException after isAssignableTo()
Posted by "Richard S. Hall" <he...@ungoverned.org>.
On 5/7/13 11:17 , Roland wrote:
> ClassCastException - not again!
>
> Hello everyone,
> after hours of investigation of my problem i resign.
>
> I embedded Apache Felix 4.3 to my host application, i use the maven blugin
> to build my project and i have 3 bundles.
>
> Bundle A (systembundle)
> Bundle B (exports a interface)
> Bundle C (implements this interface)
>
> Bundle C imports the interface and registers the implementation of the
> interface as a service.
> Bundle A imports the interface and uses this service.
>
> In the activator method of the systembundle (A) i have following code
> snippets.
You cannot use a package exported by a bundle from the system bundle. If
you need to use a service from the system bundle (i.e., in the host
application) then the service interface must be exported by the system
bundle (i.e., provided by the host application)...unless you're willing
to use reflection to access the service (pretty ugly).
At the Gogo prompt you can use "which" to see where each bundle gets a
specific class. If you test the service interface in this case, you
should see that A gets it from a different place than B and C.
>
>
> I get a ClassCastException after isAssignableTo().
>
> I checked if the interface and the implementation are fully separated.
> The imports and exports of (A,B,C) are correct.
> The classloaders are the same, namely the classloader of the bundle which
> exports the interface (B).
> I checked if the interface-package is imbedded to other bundles, but it
> exist only one version in (B).
> I checked if i'm inside or outside of OSGi. I'm definitly inside of OSGi.
>
> Have someone an idea whats going wrong? What else can I check?
> Maybe a switch to Equinox might help. Should I?
Perhaps read some more. :-)
-> richard
>
>
> Thank you so much so far.
> regards
> Roland
>
>
>
> --
> View this message in context: http://apache-felix.18485.x6.nabble.com/ClassCastException-after-isAssignableTo-tp5003252.html
> Sent from the Apache Felix - Users mailing list archive at Nabble.com.
>
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> To unsubscribe, e-mail: users-unsubscribe@felix.apache.org
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Re: Experiences with ClassCastException
Posted by Roland <wg...@ids.de>.
Hello Jan,
I introduce the framework into an existing project. Certain requirements
make it necessary to use the low-level APIs. In principle, you're right.
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Re: Experiences with ClassCastException
Posted by Jan Willem Janssen <ja...@luminis.eu>.
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Hash: SHA1
On 7/11/13 11:12 AM, Roland wrote:
> Hi, I would like to tell you about my experiences that I made
> yesterday. I had a error that occurred during integration testing
> and which is difficult to understand. But I was able to fix the
> error. Maybe I can prevent someone making the same mistake.
>
> I have a Utility-Class which is used by the Felix-Launcher
> (systembundle) as well as by some other bundles. This Utility-Class
> provides some basic functionality like catching services with
> interface-casting and error handling. Since the systembundle can
> not import packages the Utility-package has to be embedded to the
> systembundle. So far so good. At any point of time I register a
> number of services by a Bundle A. And at a later point of time I
> catch the services by calling ServiceTracker::getServices() in a
> Bundle B.
>
> public <T> T[] getServices(BundleContext bundlecontext, Class<T>
> clazz) { ServiceTracker st = new ServiceTracker(bundlecontext,
> clazz.getName(), null); st.open(); Object[] objs =
> st.getServices(); st.close(); try{ return (T[]) objs;
> }catch(LinkageError e){ ... }catch(ClassCastException e){ ... }
>
> The service-objects are instanciated by the bundle-ClassLoader of
> Bundle A. The array "Object[] objs" (see above) holding the
> service-instances is instanciated by the bootstrap-ClassLoader but
> not by the ClassLoader of Bundle A. This causes a
> ClassCastException because of two different ClassLoaders. Very
> nasty!
>
> The solution is to use Collection<T> instead of T[].
tl;drc> Why don't you use frameworks that can manage the dependencies
for you, like DS or Felix DependencyManager, instead of fiddling with
the low-level APIs?
- --
Met vriendelijke groeten | Kind regards
Jan Willem Janssen | Software Architect
+31 631 765 814
/My world is revolving around PulseOn and Amdatu/
Luminis Technologies B.V.
J.C. Wilslaan 29
7313 HK Apeldoorn
+31 88 586 46 30
http://www.luminis-technologies.com
http://www.luminis.eu
KvK (CoC) 09 16 28 93
BTW (VAT) NL8169.78.566.B.01
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Experiences with ClassCastException
Posted by Roland <wg...@ids.de>.
Hi,
I would like to tell you about my experiences that I made yesterday. I had a
error that occurred during integration testing and which is difficult to
understand. But I was able to fix the error. Maybe I can prevent someone
making the same mistake.
I have a Utility-Class which is used by the Felix-Launcher (systembundle) as
well as by some other bundles. This Utility-Class provides some basic
functionality like catching services with interface-casting and error
handling. Since the systembundle can not import packages the Utility-package
has to be embedded to the systembundle. So far so good. At any point of time
I register a number of services by a Bundle A. And at a later point of time
I catch the services by calling ServiceTracker::getServices() in a Bundle B.
public <T> T[] getServices(BundleContext bundlecontext, Class<T> clazz)
{
ServiceTracker st = new ServiceTracker(bundlecontext, clazz.getName(),
null);
st.open();
Object[] objs = st.getServices();
st.close();
try{
return (T[]) objs;
}catch(LinkageError e){
...
}catch(ClassCastException e){
...
}
The service-objects are instanciated by the bundle-ClassLoader of Bundle A.
The array "Object[] objs" (see above) holding the service-instances is
instanciated by the bootstrap-ClassLoader but not by the ClassLoader of
Bundle A. This causes a ClassCastException because of two different
ClassLoaders. Very nasty!
The solution is to use Collection<T> instead of T[].
Regards
Roland
--
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Re: ClassCastException after isAssignableTo()
Posted by Roland <wg...@ids.de>.
Thank you very much for your replys!
--
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