Re: Using an interface between two dl'ed applications

Before 'C' wants to use 'B', make sure that 'B' is loaded by 'C''s  
context classloader. One way to make this happen is to:

B = new MarshalledObject(B).get();

That way your interface will get loaded correctly

On Jan 19, 2009, at 1119AM, Gregg Wonderly wrote:

> Calum Shaw-Mackay wrote:
>> Given a system 'A' that allows objects 'B' and 'C' to be deployed  
>> to it, where 'C' has an interface dependency on 'B'. Also 'B' and  
>> 'C" are independently deployed, with potentially different  
>> codebases, but with the same interface definition (compiled) in each.
>> When 'C' requests access to 'B' via a dynamic proxy generated from  
>> the Interface declared in 'B's codebase, I get a  
>> ClassNotFoundException, I'm assuming that this is because B's  
>> classes are being declared in a different classloader to 'C's.
>> Is there any way to get around this - any particular usage of  
>> PREFERRED.LIST?
>
> The standard java URLClassLoader (or when you have no  
> PREFERRED.LIST) provides the most often correct handing for  
> interfaces by looking up the classloader chain for resolution before  
> loading locally.
>
> PREFERRED.LIST allows you to say "use my downloaded version always",  
> and in general solves the "class compatibility" issue by allowing a  
> new version of a class to be downloaded and used in preference to  
> the version that might already exist in the classloader tree.
>
> Without more information, I'd suggest that perhaps this is more  
> likely a context class loader issue.  The thread of execution that C  
> was loaded in, is not the same thread of execution that B is loaded  
> in and B's context class loader is used to resolve the interface and  
> it sees the A parent instead of the C context class loader (the  
> PreferredClassLoader that loaded C).
>
> Something like this
>
> A->C->load interface with C classloader
> A->B->load interface with B classloader
>
> So, if the interface is not visible in the "A" class loader, than  
> you must force the path to be A->C->B so that the interface is  
> loaded from C.
>
> Gregg Wonderly
>
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