We are investigating introducing Guice into a large code base. By
"large" I mean over 13,000 source Java files consisting of over 2.9
million lines of code (not including a paltry 261 unit test source
files consisting of 64,000 lines of code).
We have a mandate from on high to improve the quantity and coverage of
our unit tests and I think DI with Guice is a good fit. It's small
enough (that is, it's not Spring) that I think it will eventually be
accepted here but I've got some convincing of others to do first, so
I've got some questions that I think those that need convincing will
ask.
It would mean (incrementally, I hope!) changing classes from
instantiating their own dependees to letting Guice do it for them.
Most of our classes use the factory pattern for getting their
dependees, a la:
final CheckoutService checkoutService =
(CheckoutService)ServiceFactory.getInstance(CheckoutService.class,
ServiceFactory.CLIENT);
where the CLIENT constant signals that the factory should return an
implementation of CheckoutService that can be used from the "client"
tier of the code base (other members are WEB, meaning that the
implementation should be only used in the web tier (the servlet), and
LOCAL, meaning a POJO that lives in the app server).
Question 1: What's the best way to annotate things so that the
depender class can be unit tested with a dummy CheckoutService, but
still get a reference to the CLIENT implementation in the real
application? Do I need a RealServices module and a TestServices
module (or at least a bunch of TestFooService modules)?
Question 2: Do I create a Module per service, or lump all the Service
bindings in One Big Module? Or some other way? At last count, we've
got about 250 service interfaces.
Question 3: Where should I start making things guicy, i.e., where is
the Injector going to live? Client-side, should I start at the edge
of the object graph? Or in the main() method of my launcher class?
Or is it OK to create Injectors at the edges and move them "in" to the
graph as I guicify things?
Thanks in advance for your time.
-Russ
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