How to build an Uber JAR (Fat JAR) using SBT within IntelliJ IDEA?

Finally I totally skip using IntelliJ IDEA to avoid generating noise in my global understanding 🙂

I started reading the official SBT tutorial.

I created my project with the following file structure :

my-project/project/assembly.sbt
my-project/src/main/scala/myPackage/MyMainObject.scala
my-project/build.sbt

Added the sbt-assembly plugin in my assembly.sbt file. Allowing me to build a fat JAR :

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.12.0")

My minimal build.sbt looks like :

lazy val root = (project in file(".")).
  settings(
    name := "my-project",
    version := "1.0",
    scalaVersion := "2.11.4",
    mainClass in Compile := Some("myPackage.MyMainObject")        
  )

val sparkVersion = "1.2.0"

libraryDependencies ++= Seq(
  "org.apache.spark" %% "spark-core" % sparkVersion % "provided",
  "org.apache.spark" %% "spark-streaming" % sparkVersion % "provided",
  "org.apache.spark" %% "spark-streaming-twitter" % sparkVersion
)

// META-INF discarding
mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
   {
    case PathList("META-INF", xs @ _*) => MergeStrategy.discard
    case x => MergeStrategy.first
   }
}

Note: The % "provided" means not to include the dependency in the final fat JAR (those libraries are already included in my workers)

Note: META-INF discarding inspired by this answser.

Note: Meaning of % and %%

Now I can build my fat JAR using SBT (how to install it) by running the following command in my /my-project root folder:

sbt assembly

My fat JAR is now located in the new generated /target folder :

/my-project/target/scala-2.11/my-project-assembly-1.0.jar

Hope that helps someone else.

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For those who wants to embeed SBT within IntelliJ IDE: How to run sbt-assembly tasks from within IntelliJ IDEA?