ClassNotFoundException when adding slf4j to Akka

When adding to a Akka project I got the following error java.lang.ClassNotFoundException: akka.event.slf4j.Slf4jLogger. I double checked my configuration and the Akka documentation. The documentation says the following:

Akka provides a logger for SL4FJ. This module is available in the ‘akka-slf4j.jar’. It has one single dependency; the slf4j-api jar. In runtime you also need a SLF4J backend, we recommend Logback.

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Generating a large test file with Scala like the Linux dd command

I was writing functionality to merge download chunks yesterday. This functionality takes a file that is downloaded in chunks and mergers these chunks back into a single file. Writing the test class I did not want my test to depend on downloading a file in chunks, so I needed a way to quickly generate a number of chunks that could be merged. Under Linux the dd command is available that generates a file of a given size that contains random contents. I wrote a small helper class that does exactly this, with the extra twist that it splits the file into a number of chunks. Continue reading

Composable behavior in Scala

I continue to be amazed by what can be done with Scala. Once you start to understand the simplicity and beauty of coding in Scala it is really easy and fun. As part of my learning exercise I am implementing a multi threaded downloader. One part of the solution is a splitter. It takes a file size and splits it up into a number of chunks that can be downloaded in parallel. I have implemented a Chunk, that holds information about a chunk, as a case class and created a trait ChunkDownload that can be bolted on to this case class at runtime. This is so called composable behavior which adds functionality to the case class. Continue reading

Using scala-logger

Today I was adding logging to one of my projects. I decided to use scala-logger. I added scala-logger dependency to the build.sbt, excuted my test class and got the following error in the Eclipse console output:

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

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“value ? is not a member of akka.actor.ActorRef”

I was trying to use a Future in Akka today and got the following error message:

value ? is not a member of akka.actor.ActorRef

It turns out you have to import the akka.pattern.ask to use ‘?’. There is a implicit conversion from ActorRef to AskableActorRef.

So add the following import and you should be set to go (take note that ask does not start with a capital:

import akka.pattern.ask