More flexibility in providing services from modules?

[Alex Buckley]

Hi Tom,

Nice to see thoughts about modular services.

FYI Jigsaw's goals in this area were quite limited 
(http://openjdk.java.net/projects/jigsaw/spec/reqs/#services) and the 
static provider method was a relatively late add-on 
(http://openjdk.java.net/projects/jigsaw/spec/issues/#services).

I agree that a static provider method offers a basic level of 
indirection (e.g. multiple `provides` directives can employ the same one 
if its return type implements multiple services) but it doesn't add much 
in the way of abstraction (e.g. over the desired service). This isn't 
the only place where ServiceLoader suffers from a lack of abstraction: 
you can't parameterize services because there's no way to request an 
implementation of a parameterized service (i.e. you can't say 
`ServiceLoader.load(ServiceA<Foo>.class)`).

Frankly, we are not likely to revisit any of these limitations in the 
near future, but I think that ServiceLoader will always be a handy 
built-in option for limited use cases.

Alex

On 3/2/2019 9:19 AM, Tom De Wolf wrote:
> The current ServiceLoader mechanism and Java Modules have a limited set of
> options to provide an instance for a service from a module. Or you use the
> constructor, or you use a static 'provider' method.
>
> When interacting with frameworks like Spring this does not give a lot of
> flexibility. I described the problem statement and some ideas which could
> be considered for evolving the services support in the module system in
> this blog post:
>
> https://devcreativity.wordpress.com/2019/03/02/java-modules-wish-list-provide-services-using-lambda-functions-and-more/
>
>
> I would appreciate if some of the oracle contributors that worked on the
> module system could read the post and provide me and the community with
> some feedback if such a change could be a good idea?
>
> Thanks in advance
>
> Tom
>