An introductory tutorial to SBT

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Getting Started with SBT
Ikenna Nwaiwu

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What is SBT ?

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Objectives
• Compile and run code with SBT
• Add managed dependencies to your project
• Run tests
• Publish to a binary repository
• Use a plugin
• Assemble an run a project jar
• Open an SBT project in Intellij
• Write and SBT task

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Task 1:Write a HelloWorld file
• Create a HelloWorld programe in file “HelloWorld.scala”
• Compile it with >scalac
• Run it with >scala HelloWorld

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Task 2: Now lets use SBT for building
• Create a file build.sbt
• Add the following to your sbt file
• name := "Helloworld project”
• version := "1.0"
• - Double space between lines
• Now start sbt in the directory and run >compile and >run
• >exit

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Task 2: SBT for building – ignoring the target
directory
• SBT puts in generated classes and files in the target directory
• You can clean this directory : >clean
• If you use version control, you probably don’t want these files versioned.
Ignore them with .gitignore
$>’echo target/ ‘ > .gitignore
$>git init
$>git status

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Task 3: Lets create the project directory
structure
• Move your HelloWorlds.scala file to
the src/main/scala folder
lib/
src/
main/
resources/
scala/
java/
test/
resources/
scala/
java/

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Task 4: Add a project dependency
• Got to http://www.scalatest.org/install and
add the scalatest project dependency.
• Run > reload
• Run > update
• Run > test

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Task 5: Write a test and run it
import org.scalatest.{FunSuite, Matchers}
class HelloWorldTest extends FunSuite with Matchers {
test("Multiplication"){
val result = HelloWorld.multiply(3, 4)
result shouldBe 12
}
}
• Create a file HelloWorldTest in
src/test/scala/HelloWorldTest.scala
• Now run > test
• What do you get ?
• Implement the missing method in
HelloWorld.scala
• Now run tests again

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Task 6: Using the console and help
• The SBT console loads your project and allows
you invoke your methods and functions from
the command line
• >console
• >scala>:quit
• >help
• >help reload

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Task 6: Publishing your project locally
• Publishing a project: uploading a descriptor (Ivy file or Maven POM) and jar , to
a repository so that other projects can specify your project as a dependency.
• Add the following to your build.sbt
organization := ”com.lagosscala"
• >publishLocal
• You can now create another project and include your HelloWorld code as a
dependency with
libraryDependencies += ”com.lagosscala” %% "helloworld-project" % “1.0”

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Task 7: Adding a plugin to your project
• A plugin can be used to add more tasks to your project
• Lets add a plugin that packages our project with all the dependencies required for
executing it
• sbt assembly - https://github.com/sbt/sbt-assembly
• Create file project/assembly.sbt and add the following addSbtPlugin("com.eed3si9n"
% "sbt-assembly" % "0.14.3”)
• Now reload, update, and run >assembly
• Note the path of the created assembly jar. Can you run it with
java –jar /path/to/project-assembly.jar ?

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Task 8: Open the project in Intellij
• File > Open > Project
• Use the ‘rebuild’ in the sbt pane to reload the project when you need to.
‘Auto import’ detects file changes and does this automatically as well.

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Sbt Concepts: Settings
• An SBT project consists of an immutable map of key- value pairs
• An sbt build definition file, lists Settings (objects of Setting[T]).These are a list of transformations that can be
applied to the sbt project map. For example, they can add an entry to a map or transform an existing entry.
• The sbt build definition is a list of ‘Setting’s.
• A Setting is created by calling methods :=, +=, or ++= on a SettingKey and assigning a value.
• There are 3 kinds of Keys = SettingKey[T], InputKey[T] andTaskKey[T].
• SettingKeys – key for values computed once
• TaskKey – key for value recomputed each time
• InputKey – key for task that takes command line arguments as input
• There are built in keys that come with sbt and these are defined in sbt.Keys._
• You can create a custom key and use that for custom Settings e.g:
• lazy val helloWorld = taskKey[Unit](“My Hello World set task“)
• hello := { println("Hello World!”) }