Custom EventStream in Java

[Guillermo Szeliga]

Hi there,

I've been trying to tackle this issue on my own but I didn't succeed so far so I hope you can help. Our new architecture requires to have a whole different logging event system (independents from Akka's)  by using a LoggingAdapter instance but with a custom-tailored LogEventBus. The idea is to have actors that act as subscribers to any loggin event that's been published on our custom bus so that our own cryptography secured appenders write out all of these signed traces independently from the ordinary logging events.

Unfortunately we need to work with Java, so my first approach was to create our custom LogEventBus by extending EventStream, since it's the only implementation of a LogEventBus that I can see from the Javadocs, something like this:

public class SecureLoggerBus extends EventStream {

    /**

     * @param debug

     */

    public SecureLoggerBus(final boolean debug) {

        super(debug);

    }

}

Now, if my code is compiled using Eclipse, everything's fine and the final PoC works just as expected, but if I try to compile the same code via console, I get the following output:

[INFO] BUILD FAILURE

[INFO] ------------------------------------------------------------------------

[INFO] Total time: 2.853s

[INFO] Finished at: Thu Apr 10 14:25:24 CST 2014

[INFO] Final Memory: 13M/154M

[INFO] ------------------------------------------------------------------------

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.3.2:compile (default-compile) on project akka_lab: Compilation failure

[ERROR] /home/operador/development/workspace_experimental/akka_lab/src/main/java/com/scytl/poc/slogger/SecureLoggerBus.java:[18,7] subclassification() in akka.event.EventStream cannot implement subclassification() in akka.event.SubchannelClassification; attempting to use incompatible return type

[ERROR] found   : java.lang.Object

[ERROR] required: akka.util.Subclassification<java.lang.Object>

[ERROR] -> [Help 1]

[ERROR] 

[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.

[ERROR] Re-run Maven using the -X switch to enable full debug logging.

[ERROR] 

[ERROR] For more information about the errors and possible solutions, please read the following articles:

[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

Now, If I decide to override subclassification() as being requested with the proper return type,

public class SecureLoggerBus extends EventStream {

    /**

     * @param debug

     */

    public SecureLoggerBus(final boolean debug) {

        super(debug);

    }

    /**

     * @see akka.event.EventStream#subclassification()

     */

    @Override

    public Subclassification<Object> subclassification() {

        return (Subclassification<Object>) super.subclassification();

    }

}

The code compiles but failes at runtime.

Exception in thread "main" java.lang.NoSuchMethodError: akka.event.EventStream.subclassification()Ljava/lang/Object;

at com.scytl.poc.slogger.SecureLoggerBus.subclassification(SecureLoggerBus.java:33)

at akka.event.SubchannelClassification$class.akka$event$SubchannelClassification$$subscriptions(EventBus.scala:131)

at akka.event.EventStream.akka$event$SubchannelClassification$$subscriptions$lzycompute(EventStream.scala:26)

at akka.event.EventStream.akka$event$SubchannelClassification$$subscriptions(EventStream.scala:26)

at akka.event.SubchannelClassification$class.publish(EventBus.scala:168)

at akka.event.EventStream.publish(EventStream.scala:26)

at akka.event.EventStream.subscribe(EventStream.scala:45)

at com.scytl.poc.slogger.main.Main.main(Main.java:38)

 I'm currently using Akka 2.3.2.

Any ideas? Does it have to do the fact that suclassification is an implicit val expected somewhere?

Any hint will be appreciated. Thanks!

[Patrik Nordwall]

Use the classes in akka.event.japi.*

The classes in akka.event.* is the Scala API.

Cheers,

Patrik

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[Guillermo Szeliga]

I've checked the Java API but I can't figure out how to build up a custom LoggingBus from scratch that can be passed to a LoggingAdapter instance. All the buses implementations do not implement such "interface".

Am I loosing my time or is there any way of achieving it using Java?

Cheers and thanks for the patience!

[Patrik Nordwall]

On Wed, Apr 23, 2014 at 3:37 PM, Guillermo Szeliga <gsze...@gmail.com> wrote:

I've checked the Java API but I can't figure out how to build up a custom LoggingBus from scratch that can be passed to a LoggingAdapter instance. All the buses implementations do not implement such "interface".

What do you need to do with your custom event bus? Should it be as the ActorSystem.eventStream? You can subscribe to event classes (sub-classes)? The you should start with http://doc.akka.io/docs/akka/2.3.2/java/event-bus.html#Subchannel_Classification

That example operates on strings, and you want it to operate on classes. For example isSubclass can be implemented with y.isAssignableFrom(x), classify is implement with event.getClass()

Regards,

Patrik

[Konrad Malawski]

We also found 2 pretty cool blog posts (by Ben Howell) explaining akka's event buses a bit today, see: http://www.benhowell.net/examples/2014/04/18/scala-and-the-akka-eventstream/

-- 

Konrad `ktoso` Malawski