Thursday, January 5, 2012

Shrinked Scala jar from proguarded files

Ok short post how to shorten package time when using Scala.

So after you've run your packaging with proguard you should have your scala files under:

so what you want to do is run the following:
jar cvf shrinked-scala-1.0.jar scala

This will create a file called shrinked-scala-1.0.jar which contains all the Scala files and methods you've used in your project so far.

Next we'll add the file to our local maven repository:
mvn install:install-file -Dfile=./shrinked-scala-1.0.jar -DgroupId=com.punchwolf.scala -DartifactId=shrinked-scala -Dversion=1.0 -Dpackaging=jar

Now that we have the package in your repository we can create a new profile that uses the original Scala for compilation only but takes the shrinked version in to the package as a dependency.

The above profile uses the original scala-lang as provided scope (used in compilation) and the shrinked is used in compilation scope (is packaged in the APK).

what you'll also need to do is to have a default profile that uses proguard and the scala-lang in compilation scope.

now that you have these separated, you can run the following:
mvn clean package -P hacked

Now the compilation should be done without the proguard and your new package should be executable in your phone.

The drawback is that if you use a new Scala feature that you don't have in your shrinked-scala, the program will fail saying that there's no class found. So you'll need to run the proguard profile package again and generate the shrinked-scala.jar from the proguarded scala files.

This is not very useful in the early stage of development, but it's very useful when you have pretty stable set of Scala features you use in your project or if you are debugging something.


  1. If you're early in development and using Eclipse, you might want to check out my plugin for doing something similar. It's at It's basically a detection system for figuring out if you've changed any calls to the scala library, and if not, just use the proguard outfile from a previous run that matched.

    One of the things on my todo list is to make it's api usable from maven, but since I don't use maven it's not gotten very far.

  2. Thanks for the heads up. Our project is nearing first public release, around 7500 lines of Scala. When we started like 8 months ago, Intellij Idea's Scala plugin was considerably better than what was available for Eclipse so we have stuck with Intellij.