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Posted to users@felix.apache.org by Roland <wg...@ids.de> on 2013/07/11 11:12:00 UTC
Experiences with ClassCastException
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: 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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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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