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Gradle Goodness: Using CopySpec with Tasks

To define a Copy task we specify the files we want to copy and to which directory. This definition is a CopySpec instance. It contains the rules that defines what we want to copy. The archive tasks Jar, Zip and Tar also use a CopySpec instance. When we create a task of type Copy we get a task object that ...

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Gradle Goodness: Using and Working with Gradle Version

To get the current Gradle version we can use the gradleVersion property of the Gradle object. This returns a string value we can use for displaying the values. If we want to compare Gradle versions we can use the GradleVersion object. With this class we can get the current version, but we can also compare Gradle versions. This can be ...

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Spark: Parse CSV file and group by column value

I’ve found myself working with large CSV files quite frequently and realising that my existing toolset didn’t let me explore them quickly I thought I’d spend a bit of time looking at Spark to see if it could help. I’m working with a crime data set released by the City of Chicago: it’s 1GB in size and contains details of ...

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First steps with REST, Spray and Scala

On this site you can already find a couple of articles on how to do REST with a multiple of different frameworks. You can find an old one on Play, some on Scalatra and I even started an (as of yet unfinished) series on Express. So instead of finishing the series on Express, I’m going to look at Spray in ...

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Akka Notes – Actor Supervision – 8

Failures are more like a feature among distributed systems. And with Akka’s let it crash fault tolerance model, you could achieve a clear separation between your business logic and your failure handling logic (supervision logic). All with very little effort. It’s pretty amazing. This is the topic of our discussion now. Actor Supervision Imagine a method call stack and the ...

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Using Groovy for Bash (shell) Operations

Recently I needed to create a groovy script that deletes some directories in a Linux machine. Here’s why:                   We have a server for doing scheduled jobs. Jobs such as ETL from one DB to another, File to DB etc. The server activates clients, which are located in the machines we want ...

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Clustering reactmq with akka-cluster

In the last two posts on reactmq, I described how to write a reactive, persistent message queue. The queue has the following characteristics:                   there is a single broker storing the messages, with potentially multiple clients, either sending or receiving messages provides at-least-once-delivery; receiving a message blocks the message; unless it is ...

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Akka Notes – DeathWatch – 7

When we talked about Actor lifecycle, we saw that Actors could be stopped by various means (using ActorSystem.stop or ActorContext.stop or sending a PoisonPill – there’s also the Kill and the gracefulStop). Whatever reason an Actor dies, there are cases when a few other actors in the system would like to know about it. Let’s take a trivial example of ...

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