6. Build Tools for Scala

In this section, we provide a brief overview of build tools for Scala. In general, build tools support the build process in several ways:

structured representation of the project dependency graph
management of the build lifecycle (compile, test, run)
management of external dependencies

6.1. Why Use a Build Tool?

When using the Java or Scala command-line tools, the developer is responsible for setting the dreaded classpath. This can quickly become unwieldy when dependencies even as simple as JUnit are involved, so this is not something you would usually want to do manually.

6.2. Brief History of Build Tools

Unix make, Apache ant: These tools manage the build lifecycle but not external dependencies.
Apache maven: This tool also manages external dependencies but requires a lot of XML-based configuraration.

      <dependency>
              <groupId>org.restlet</groupId>
              <artifactId>org.restlet.ext.spring</artifactId>
              <version>${restlet.version}</version>
      </dependency>

Apache ivy, Gradle, Scala’s Simple Build Tool (sbt) [http://www.scala-sbt.org], etc.: These tools emphasize convention over configuration in support of agile development processes. sbt is compatible with ivy and designed primarily for Scala development. For example, ivy uses a structured but lighter-weight format:

      <dependency org="junit" name="junit" rev="4.11"/>

6.3. sbt

In the simplest case, sbt does not require any configuration and will use reasonable defaults. The project layout is similar to that used by Maven:

Production code goes in src/main/scala.
Test code goes in src/test/scala.

sbt supports two configuration styles, one based on a simple Scala-based domain-specific language, and one based on the full Scala language for configuring all aspects of a project.

6.3.1. build.sbt format

A minimal sbt build.sbt file would look like this. The empty lines are required, and the file must be placed in the project root folder.

  name := "integration-scala"

  version := "0.0.2"

Additional dependencies can be specified either one at a time

  libraryDependencies += "com.novocode" % "junit-interface" % "0.10" % "test"

or as a group

  libraryDependencies ++= Seq(
    "org.scala-lang" % "scala-actors" % "2.10.1",
    "com.novocode" % "junit-interface" % "0.10" % "test"
  )

6.3.2. Build.scala format

Examples of more complex Scala-based project configurations can be found in these examples:

Android click counter app [https://bitbucket.org/loyolachicagocs_plsystems/clickcounter-android-scala/src/tip/project/]
Prime checker web service [https://bitbucket.org/loyolachicagocs_distributed/primenumbers-spray-scala/src/master/project/]

6.4. Plugin Ecosystem

sbt includes a growing plugin ecosystem. Key examples include

sbteclipse [https://github.com/typesafehub/sbteclipse]: automatically generates an Eclipse project configuration from an sbt one.
sbt-start-script [https://github.com/sbt/sbt-start-script]: generates a start script for running a Scala application outside of sbt.

The IntelliJ IDEA Scala plugin also integrates directly with sbt.

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