Hi all:
I was wondering – does anyone have any experience with or patterns for
integrating Clojure with existing Java dependency injection frameworks?
I’m working with the LensKit framework [1] for a MOOC and it uses a
JSR-330/javax.inject dependency-injection framework named `grapht` [2]
for, well, everything. In some examples dependency-injection is even
used to provide input data file paths (!). As far as I can tell, the
injection happens entirely via invoking some sort of concrete,
user-provided, annotated constructor which accepts injected instances on
(potentially annotated) constructor parameters.
My thoughts thus far have centered on two basic potential approaches:
1. Implement small Java stubs with appropriately-annotated constructors
for every injection point. The downside is that these stubs are
(probably) not very reusable. Injected instances are only injected at
the constructor parameters, so needing a different set of injected
instances requires a different class/constructor.
2. Dynamically generate stub classes exposing constructors which accept
some arbitrary per-class set of inject-able parameters. There might be
an easier way to do it, but that’s the approach I’ve tried out thus-far
using ASM and the Clojure dynamic class loaders to produce “Provider”
factory classes:
https://github.com/llasram/esfj
The largest problem with this approach is that the actual factory
implementation still needs to be injected somehow. I thought about
stashing a function in a Var linked to the class, but have instead just
made the implementation function itself another inject-able IFn
parameter. This avoids namespace-abuse, but also means injecting
Clojure implementations involves doing *more* dependency injection than
with plain Java, which doesn’t seem right.
Thoughts?
[1] http://lenskit.grouplens.org/
[2] https://github.com/grouplens/grapht
-Marshall
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