A small Scala library for using JSON-based configuration files.
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You probably don't need another data format, right?

Fig is a very small Scala library which makes it easy to read data out of JSON-based configuration files, with full support for Javascript-style comments. (We're not barbarians here.)


  • Scala 2.8.1 or 2.9.0
  • Jerkson 0.2.1


  • enough structure for most purposes
  • fairly human-readable
  • very well supported
  • easy to use with configuration management systems like Chef or Puppet

How To Use

First, specify Fig as a dependency:

val codaRepo = "Coda Hale's Repository" at "http://repo.codahale.com/"
val fig = "com.codahale" %% "fig" % "1.1.3"

Second, write your config file:

    /* Config allows you to use C-style comments.
     * This, for example, is a block comment.
    "parent": { // Comments can terminate a line, too.
        "child": {
            "url": "http://example.com",
            // We don't care about comments inside string literals.
            "splody-string": "An-a one an-a two an-a // /*wah*/ YAY",
            "count": 100,
            "names": ["One", "Two", "Three"],
            "mapped": {
                "1": 1,
                "2": 2,
                "3": 3
            "doubly-mapped": {
                "1": [1, 2, 3],
                "2": [2, 3, 4],
                "3": [3, 4, 5]

Third, load your config file:

import com.codahale.fig.Configuration

val config = new Configuration("myapp/config.json")

You can also create a new Configuration instance from a Source or an InputStream.

Fourth, read values from it:

// Load a value directly.
val port = config("http.port").as[Int]

// Load a value as an option.
val uri = config("http.uri").asOption[Int]

// Load a value or a default value.
var server = config("http.server").or("Fig-Powered")

// Load a list of values.
val numbers = config("http.numbers").asList[Int]

// Or a map of values (key are required to be strings)
val properties = config("http.resource").asMap[String]

// Hell, even load a case class.
case class ResourceConfig(name: String, uri: String)
val resource = config("http.resource").as[ResourceConfig]

// Defy type erasure for lists!
val numbers = config("http.more-numbers").asMap[List[Int]]


Copyright (c) 2010 Coda Hale

with contributions from

  • Bryan J Swift

Published under The MIT License, see LICENSE