On 19/03/2017 21:48, Gunnar Morling wrote:
Is there a way to execute some code when a module is "activated" or
resolved? I'm not sure what the current word is in Jigsaw terms, but I
hope it becomes clearer in the following.
To overcome the issue of dependency cycles between slf4j API and
implementations (when treating them as named modules by adding module
descriptors, as required for using slf4j in a modular runtime image),
I've been experimenting with injecting a class into the slf4j.api
module which establishes the read from API to impl dynamically:
public void addImplReads() {
Module apiModule = org.slf4j.Logger.getClass().getModule();
apiModule.addReads( apiModule.getLayer().findModule(
"slf4j.simple").get() );
}
This technique requires "someone" to call this method, before invoking
any method on the slf4j API. That could be done by the user's
application, but it'd be much more user-friendly if this could happen
automatically if the slf4j API module is resolved. Hence I'm trying to
figure whether one can register a callback or similar and be notified
in that case.
There isn't any notification/callback. Also it's not clear to me that
injecting code into SLF4J is the right thing to do (it feels like hacking).
If I were a SLF4J maintainer then I think I would re-visit how the API
locates the logging framework binding. Specifically I would look to
migrate it to services. So rather than each binding a
org.slf4j.impl.StaticXXXX classes, it would instead provide an
implementation of a service type that SLF4J puts in an exported package.
It may be that cleaning up this area can be done without any impact to
user code and I would expect the issue of the simple binding to just
fall out of the wash.
-Alan.
