Starting Akka Project With SBT 0.10

I was starting with Akka project with SBT but found that the latest SBT is quite different from before.

I tried to create AKKA project with latest SBT but got stuck. Old SBT used to ask to create a new project in case it did not find any in the directory. With new SBT it is not the case. If you want to know how to go about creating new Akka project with SBT read on.

After installing SBT if we type in sbt in the command prompt in an empty directory, this is what we are likely to see.

In order to create project execute the following commands in the sbt session.

> set name := "AkkaQuickStart"
> set version := "1.0"
> set scalaVersion := "2.9.0-1"
> session save
> exit

We should get the following output if we type the above mentioned commands in sbt session.

SBT creates files and directories when we executed the commands. It creates build.sbt and it contains the same values we typed in sbt session. Other directories like target and project are of little consequence to us.

Project directory will become important later when we will try to add sbteclipse plugin. My project directory contains the following subdirectories and files.

Getting Started With Scala

I and Vikas presented on “Getting Started With Scala” few years back. It was presented at OSS camp 2009 in New Delhi. I still remember the interest it created at the conference.

Today I happened to have a look at it on Slideshare. Looking at the number of views it seems to be doing good. Out of my previous employer presentations its having highest hits. Scala is really doing good in terms of popularity.

Presentation is still old. To get started concepts are still the same. Enjoy the presentation…

Working With Scala Collections

We have a monthly iBAT (Inphina Beer and Technology Sessions). We look forward to this day and it was Scala day this time. I presented on Scala collections.

Scala collection is elegant and concise. Scala Collections like java is object-oriented and we can work with generic types. It is optionally persistent i.e can be mutable and immutable. It provides higher order methods like foreach, map and filter.

Scala collections follow uniform return type principle. Which basically means that when you perform an operation on a collection they return a collection of the same type.

The root Trait in Scala collections is Traversable. It may take some time to get used to it as Scala collections root Traits like Traversable have a big bunch of methods.

The for notation is more readable. It is basically like a for loop with a return type. Look for yourself how readable it is compared to the original code.

This code listing is without a for notation

scala> val listOfNumbers = List(1, 2, 3)
listOfNumbers: List[Int] = List(1, 2, 3)

scala> val flattenedListOfNumbers = listOfNumbers flatMap (0 to _)
flattenedListOfNumbers: List[Int] = List(0, 1, 0, 1, 2, 0, 1, 2, 3)

After using for notation

scala> val listOfNumbers = List(1, 2, 3)
listOfNumbers: List[Int] = List(1, 2, 3)

scala> val flattenedList = for(number <- listOfNumbers; range <- 0 to number) yield range
flattenedList: List[Int] = List(0, 1, 0, 1, 2, 0, 1, 2, 3)

One more interesting thing we can do with a Map is that we can reverse key and value with the following code

scala> val aMap = Map("India" -> "Delhi", "France" -> "Paris", "Italy" -> "Rome")
aMap: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map(India -> Delhi, France -> Paris, Italy -> Rome)

scala> val reverseMap = aMap map{case(k, v) => (v, k)}
reverseMap: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map(Delhi -> India, Paris -> France, Rome -> Italy)

scala> val alsoReverseMap = for((k, v) <- aMap) yield (v -> k) 
alsoReverseMap: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map(Delhi -> India, Paris -> France, Rome -> Italy)

Reference were from Martin’s Odersky talk on Future Proofing Collections and Scala Collections API documentation. Enjoy the presentation …

Working With Scala Test

Scala Test is an open source Test framework for the java platform. With Scala test we can either test java or Scala code. It integrates with popular existing tools like JUnit, TestNG and it is designed to do different styles of testing like Behavior Driven Design for example.

Let’s have a look at a simple JUnit4 Test in Scala Test

package com.inphina.ibat.junit

import org.scalatest.junit.AssertionsForJUnit
import org.junit.Assert._
import org.junit.Test
import  org.junit.Before

class SimpleJunit4Demo extends AssertionsForJUnit {

  var sb: StringBuilder = _

  @Before def initialize() {
    sb = new StringBuilder("Welcome To ")
  }

  @Test
  def verifyEasy() {
    sb.append("ScalaTest!")
    assertEquals("Welcome To ScalaTest!", sb.toString)
  }

}

This Test implementation is not very different from a normal JUnit Test we are accustomed to. In order to understand ScalaTest there are three concepts we need to be aware of.

• Suite: A collection of tests. A Test is anything that has a name and can succeed or fail
• Runner: ScalaTest provides a Runner application that can run Suites of Tests
• Reporter: As Tests are run events are fired to a reporter, it takes care of presenting results back to the user

Let’s have a bit more detailed look at the Suite which is a Trait.