override module with an alternative implementation in the child layer

[Milen Dyankov]

In response to a question posted on this list [1] some time ago, Alan
Bateman stated "You can override *any* module (except java.base) with an
alternative implementation in the child layer". Is that true for the
standard JDK modules? If so, is there any documentation / code samples that
explains how?

The obvious naive approach to load standard module in a layer:

ModuleFinder finder = ModuleFinder.ofSystem();

ModuleLayer bootLayer = ModuleLayer.boot();

Configuration cf = bootLayer.configuration().resolve(finder,
ModuleFinder.of(), Set.of("java.sql"));

ClassLoader scl = ClassLoader.getSystemClassLoader();

ModuleLayer layer1 = bootLayer.defineModulesWithOneLoader(cf, scl);


results in

Exception in thread "main" java.lang.LayerInstantiationException: Class
loader (instance of): jdk/internal/loader/Loader tried to define prohibited
package name: java.util.logging

Regards,
Milen

[1]
http://jigsaw-dev.1059479.n5.nabble.com/Whitelisting-modules-in-layers-td5717573.html#a5717574