Hey,
As you know we do not have names for Services, and especially on the
@Service injection there is no way to specify "id" or "name" of the
service to be injected if there are several ones that meet the requirements.
There are mainly two ways to get around this. Either one can inject
Iterable<ServiceType> and select one from the list in the actual code,
or one can add a Service of the specified type to the Module in the
Assembler and have it do the filtering. Here's an example of how it
could work:
module.addObjects( ServiceConsumer.class );
module.addServices( TestService.class ).
providedBy( ServiceIdFilter.class ).
setServiceAttribute( String.class,
TestServiceComposite2.class.getSimpleName() );
module.addServices( TestServiceComposite1.class,
TestServiceComposite2.class);
---
So, even if there are two TestServiceComposite's registered, which both
implement TestService, I add another one before them which does a lookup
on the given type (TestService) and finds the one with the given id.
This can be expanded to more advanced checks, to test for other
attributes or similar. In this case there is no need for the
ServiceConsumer to do any selection itself, it just does @Service
TestService and it will have the "correct" one injected.
This approach does not handle the case that different injection points
in the same module wants different services injected, i.e. they will all
get the same.
Is this good enough? Can you see any scenarios where you would want/need
even more control? And if so, any suggestions on how that should work?
Note that the above pattern can also be used for Service proxy/policy
purposes, e.g. instead of id filtering the custom provider could select
the first Service in the list to begin with and on exception or
unavailability move to the next Service available.
/Rickard
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