ClassLoader.getResources(String)

[Stephen Colebourne]

On 7 March 2018 at 12:59, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> You've dismissed services but I would expect it to provide a nice solution.
> The service interface might be very simple, something like:
>
> public interface LeapSecondDataProvider {
>     LeapSecondData data();
> }

Configuration and code are two very different things. Asking projects
and end users to write code for something that should be config is a
huge no-no.

My view is that JPMS has made using configuration files, especially
for libraries, a lot harder. This is a step back in usability. Just so
we are clear, for leap seconds I will now have to ask users to
manually register them using an API where previously they just added a
file. But for OpenGamma Strata, the configuration files are much more
complex and certainly unsuited to be code, even if the backwards
compatibility issues were acceptable. (This is a pattern I've used for
configuration for many years)

Effectively what is needed is another way for a library to be informed
of the presence of the calling application. One possible solution to
this would be to allow users to write module initialization code in
module-info.java. Then an application coder would have a solid
reliable place to put code that registers the additional configuration
files with the low-level library. Something like:

module com.foo.app {
  requires org.threeten.extra;

  init(ModuleInitContext context) {
    UtcRules.registerLeapSecondFile("/com/foo/app/LeapSeconds.txt");
  }
}

PS. ServiceLoader is a pain to use in Java 9 too. As a library doesn't
know whether it will run as a named module or on the classpath, I have
to duplicate the service loader configuration - once in
META-INF/services and once in module-info.java, which is horrible. It
also means that the provide() static method is a feature that cannot
be used by libraries.

Stephen