Scala – how to set main class in SBT 0.13 project

sbtscala

Could you guys please explain to me how to set main class in SBT project ? I'm trying to use version 0.13.

My directory structure is very simple (unlike SBT's documentation). In the root folder I have build.sbt with following content

name := "sbt_test"

version := "1.0"

scalaVersion := "2.10.1-local"

autoScalaLibrary := false

scalaHome := Some(file("/Program Files (x86)/scala/"))

mainClass := Some("Hi")

libraryDependencies ++= Seq(
    "org.scalatest" % "scalatest_2.10" % "2.0.M5b" % "test"
)

EclipseKeys.withSource := true

And I have subfolder project with single file Hi.scala which contains following code

object Hi {
  def main(args: Array[String]) = println("Hi!")
}

I'm able to compile it by calling sbt compile but sbt run returns

The system cannot find the file C:\work\externals\sbt\bin\sbtconfig.txt.
[info] Loading project definition from C:\work\test_projects\sbt_test\project
[info] Set current project to sbt_test (in build file:/C:/work/test_projects/sbt_test/)
java.lang.RuntimeException: No main class detected.
        at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last compile:run for the full output.
[error] (compile:run) No main class detected.
[error] Total time: 0 s, completed Apr 8, 2013 6:14:41 PM

Best Answer

You need to put your application's source in src/main/scala/, project/ is for build definition code.

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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
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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(".")).
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val sparkVersion = "1.2.0"

libraryDependencies ++= Seq(
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// META-INF discarding
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}

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.

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

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