Scala Cookbook

18.14. Deploying a Single, Executable JAR File

Problem

You’re building a Scala application, such as a Swing application, and want to deploy a single, executable JAR file to your users.

Solution

The sbt package command creates a JAR file that includes the class files it compiles from your source code, along with the resources in your project (from src/main/resources), but there are two things it doesn’t include in the JAR file:

• Your project dependencies (JAR files in your project’s lib folder, or managed dependencies declared in build.sbt).

• Libraries from the Scala distribution that are needed to execute the JAR file with the java command.

This makes it difficult to distribute a single, executable JAR file for your application. There are three things you can do to solve this problem:

• Distribute all the JAR files necessary with a script that builds the classpath and executes the JAR file with the scala command. This requires that Scala be installed on client systems.

• Distribute all the JAR files necessary (including Scala libraries) with a script that builds the classpath and executes the JAR file with the java command. This requires that Java is installed on client systems.

• Use an SBT plug-in such as sbt-assembly to build a single, complete JAR file that can be executed with a simple java command. This requires that Java is installed on client systems.

This solution focuses on the third approach. The first two approaches are examined in the Discussion.

Using sbt-assembly

The installation instructions ...