Proper way to inject dependencies into clustered persistent Akka actors? - scala

Question

I'm using Akka Persistence with Cluster Sharding. What is the proper way to provide dependencies into such PersistentActor-s?
As far as I understand, passing them as constructor arguments is not possible, as Cluster Sharding is creating these actors.
Using Spring/Guice/etc. is not idiomatic Scala (and possibly has other issues (?)).
Using an object to implement a singleton makes for cumbersome testing and seems bad style.
What is the proper way?
P.S. If you plan to suggest the Cake pattern, please provide sample code in this specific Akka Persistence Cluster Sharding context.

Answer 1

UPDATED VERSION:
the solution I offered earlier did not allow to mock services of the actor under test in unit test cases.
I am using instead one solution offered on that article http://letitcrash.com/post/55958814293/akka-dependency-injection that is called "aspect weaving" and that consists of injecting the dependencies in the actor using aspect oriented programming.
This solution can be used to inject Spring dependencies on any bean not controlled by Spring container (potentially useful for legacy code).
A full example is provided by the above article: https://github.com/huntc/akka-spring/blob/f137c98b621517301f636e6ea03519388fcd5fff/src/main/scala/org/typesafe/Akkaspring.scala
And to enable aspect weaving in a spring based application you should check the documentation on Spring doc
In my case, on a jetty application server, it consists of using the spring agent and setting it in the jvm arguments.
As far as tests are concerned, I :
created setters for the injected services
created basic configuration for my actors with null beans referenced for my dependencies
instantiated the actor in my test case
replace the actor's services with mocks
run the actor's inner methods and check the results, actor's state or calls to dependencies
ORIGINAL:
I am using Akka in a Spring Application to enable clustering. At first
it raises the following issue: you cannot inject spring managed
dependencies in the actor constructor, as you said. (it tries to
serialize the application context and fails)
So I created a class that holds the application context and provides a
static method to retrieve beans I need. I retrieve the bean only if I
need it, this way:
public void onReceive{
if (message instanceof HandledMessage) {
(MyService) SpringApplicationContext.getBean("myService");
...
}
}
It's not conventional but it does the job, what do you think? Hope
otherwise it might help another one.