Example code in JDK8 requiring change for modular function

[Alan Bateman]

On 07/05/2012 04:36, David Holmes wrote:
> On 7/05/2012 12:17 AM, Alan Bateman wrote:
>> On 06/05/2012 13:36, David Holmes wrote:
>>> :
>>>>
>>>> When running in "modular mode" the system class loader is the class
>>>> loader of the entry module, where as what we really want to use is
>>>> the class loader of the callee (the class loader used to load Files).
>>>
>>>
>>> The system class loader needed not be the classloader of the callee.
>>> So if we expect this to use the loader of the callee then the code is
>>> broken regardless of module-mode.
>> This code works as specified, if you have a custom file type detector
>> then you put it on the system class path and it will be located.
>
> Okay - then the expectation is _not_ to use the loader of the callee 
> at all. That's fine.
I think caller vs. callee has got a bit confused in this discussion. For 
ServiceLoader usages then the important code is the code that is 
invoking ServiceLoader. So assume we are running with modules and the 
application invokes Files.probeContentType to probe the type of a file. 
This gives us application -> Files.probeContentType -> ... 
Files$FileTypeDetectors$1.loadInstalledDetectors -> ServiceLoader. If 
the code is changed to use loadInstalled (one of the choices, not 
necessarily the best choice here) then ServiceLoader.loadInstalled will 
need to look at the caller frame. In this case the caller (of 
ServiceLoader.loadInstalled) is in the base module and the base module 
will have declared that it requires service 
java.nio.file.spi.FileTypeDetector. At configuration time then the base 
module will have been linked with all modules that provide 
implementations of the service so everything works as expected. 
Hopefully this is clearer now.

-Alan.