Scala - Use Multiple Configs in Sbt Project

Ref:

[1] - play test 実行時に指定したconfファイルを読み込む

[2] - github - typesafehub/config

---

Using config file absolutely make your life easier to deploy, debug, and test your applications.
Sometimes people want to use different config file to run dev or run prod, Sometimes people just want to use different config to test.

So, I'm going to show how to use multiple config files in sbt project.
In this post, I create minimal project by using typesafe's activator, and I strongly command this tool to create small and clean project with least dependency to train skills.

Normal way to use config in sbt project

Firstly, create simple sbt Scala project. I created it by using activator:

./activator new

And then follow the command wizard to choose minimal-scala as your project type, and fill up the project name.

To load config file, you will need one extra dependency: typesafe's config.

And following to the build.sbt file under the root directory of the project.

resolvers += "Typesafe Repo" at "http://repo.typesafe.com/typesafe/releases/"

libraryDependencies += "com.typesafe" % "config" % "1.2.1"

Now your build.sbt file should looks like:

name := """project-name"""

version := "1.0"

scalaVersion := "2.11.1"

resolvers += "Typesafe Repo" at "http://repo.typesafe.com/typesafe/releases/"

// Change this to another test framework if you prefer
libraryDependencies += "org.scalatest" %% "scalatest" % "2.1.6" % "test"

libraryDependencies += "com.typesafe" % "config" % "1.2.1"

Ok, by now, you could use a module named ConfigFactory in your project to load your config files.

It's time to add your own config file.

Add application.config under your src/main/resources, and write some random configs into it.
Here is mine:

test.text1="1"
test.text2="2"
test.text3="3"

To check whether this config file could be properly loaded, write a simple program to check it out:

import com.typesafe.config.ConfigFactory

object Hello {
  def main(args: Array[String]): Unit = {
    println("Hello, config!")
    val configText1 = ConfigFactory.load().getConfig("test").getString("text1")
    val configText2 = ConfigFactory.load().getConfig("test").getString("text2")
    val configText3 = ConfigFactory.load().getConfig("test").getString("text3")
    println(configText1)
    println(configText2)
    println(configText3)
  }
}

When run this script, it will give:

Hello, config!
1
2
3

Use config in your test

In most cases, people use a set of different configs in their tests.
It would be great if one can just replace some of the configs in the src/main/resources/application.conf and keep the others.

Actually, when run sbt test, sbt will first look for src/main/resources/application.config and then use src/test/resources/application.confg to overwrite configs in the first one.

Note: sbt will do the overwrite even if you not use include "application.config" in the src/test/resources/application.config.

To check that, add new test case under src/test/scala in your project:

import com.typesafe.config.ConfigFactory
import org.scalatest._

class HelloSpec extends FlatSpec with Matchers {
  "Hello" should "have tests" in {
    val configText1 = ConfigFactory.load().getConfig("test").getString("text1")
    val configText2 = ConfigFactory.load().getConfig("test").getString("text2")
    val configText3 = ConfigFactory.load().getConfig("test").getString("text3")
    println(configText1)
    println(configText2)
    println(configText3)

    true should be === true
  }
}

Then add config file for the test as src/test/resources/application.conf.

test.text2="22"

When you run sbt test you will get this as expected:

1
22
3

Use specific config file

Normally, you can specify the config file by use sbt parameter -Dconfig.file or -Dconfig.resource.(for detailed information please refer to this doc)

But in team work, you probably want this to be static, and use the file you have specified whenever and whoever run sbt test.
In that case, you need to put a extra in your build.sbt:

fork in Test := true // allow to apply extra setting to Test

javaOptions in Test += "-Dconfig.resource=test.conf" // apply extra setting here

And then, put your test.conf to the src/test/resources/test.conf:

include "application.conf"

test.text3="333"

Note that in this time you will have to use include "application.conf".

And this time when you run sbt test, you will get:

1
22
333

That is because the sequence of config files overwrite each others is:

src/test/resources/test.conf
src/test/resources/application.conf
src/main/resources/application.conf

Note that no matter you like or not, once you include the "application.conf",
the sbt will first try to find src/test/resources/application.conf.
If that does not exist, then it will find src/test/resources/application.conf.

Even if you delete the src/test/resources/application.conf, the src/main/resources/application.conf is still in the system.

Here is the result if there is no src/test/resources/application.conf in the project:

1
2
333