River-300 Modular Build - Preferred Classes.

[Peter Firmstone <ji...@zeus.net.au>]

Preferred classes are used for the proxy's currently, the jsk-dl.jar in 
our current build is included in proxy codebase annotations, this is to 
ensure that com.sun.* namespace implementation classes are loaded by the 
proxy ClassLoader. 

In the modular build, we have a dependency relationship where 
river-lib.jar depends on river-dl.jar to avoid duplication of source files.

This means that river-lib.jar and river-dl.jar (it has been suggested to 
rename it to river-api.jar), will be on the classpath.

However river-dl.jar must continue to be part of the codebase annotation 
for proxy's to ensure that proxy's load the com.sun.* namespace (except 
for classes which are not preferred), into the proxy classloader to 
prevent codebase annotation loss and to allow those implementation 
classes to change, such that the proxy's don't have to share the same 
implementation version as the platform.

Non preferred classes however are loaded from the classpath if 
available, or loaded into the proxy classloader if they are unavailable 
on the classpath.

This means we are free to re-implement preferred classes in 
river-lib.jar and river-dl.jar over time, without worrying much about 
backward compatibility, since different versions can be selected by 
service implementers.

There are classes that are currently not preferred (which will be loaded 
by the application classloader if available) we should investigate 
moving these to the platform.jar or another aptly named jar, then we 
won't have to list them as not preferred and simply list the preferred 
namespaces in our proxy jar files.

Regards,

Peter.