CaseConfig

CaseConfig is an extension for Typesafe Config that provides a safer and cleaner approach to reading in a configuration file. CaseConfig's model-driven approach of parsing configuration into types provides validation for "required" fields and field types for free. It also provides a clearer way of accessing configuration fields using case class values instead of Config objects of Config objects, which is analogous to dealing with a heterogeneous Map of Maps.

There isn't much to it, so here are some exampels:

Example 1: Get a required String

Good times when the configuration field exists:

import com.pellucid.caseconfig._
import com.typesafe.config.ConfigFactory

val config = ConfigFactory.parseString(
        """
        |{
        |   myfield = "my value"
        |}
        """.stripMargin)

val myfield = config.get[String]("myfield")

Result: myfield = "my value"

An error when it does not exist:

import com.pellucid.caseconfig._
import com.typesafe.config.ConfigFactory

val config = ConfigFactory.parseString(
        """
        |{
        |   myfield = "my value"
        |}
        """.stripMargin)

val missing = config.get[String]("missing")

Result:

com.typesafe.config.ConfigException$Missing: No configuration setting found for key 'missing'
  at com.typesafe.config.impl.SimpleConfig.findKey(SimpleConfig.java:124)
  at com.typesafe.config.impl.SimpleConfig.find(SimpleConfig.java:145)
  at com.typesafe.config.impl.SimpleConfig.find(SimpleConfig.java:159)
  at com.typesafe.config.impl.SimpleConfig.find(SimpleConfig.java:164)
  at com.typesafe.config.impl.SimpleConfig.getString(SimpleConfig.java:206)
  at com.pellucid.caseconfig.types.Types$StringType$.get(Types.scala:195)
  at com.pellucid.caseconfig.types.Types$StringType$.get(Types.scala:194)
  at com.pellucid.caseconfig.package$TypelevelConfig2CaseConfig.get(package.scala:52)
  ... 46 elided

Example 2: Get an optional string

To specify that a configuration value is optional, its type should be an Option of its value type. If the field doesn't exist it results in a None rather than a validation error.

import com.pellucid.caseconfig._
import com.typesafe.config.ConfigFactory

val config = ConfigFactory.parseString(
        """
        |{
        |   myfield = "my value"
        |}
        """.stripMargin)

val myfield = config.get[Option[String]]("missing")

Result: myfield = None

Example 3: Get a case class from a configuration object

Notes:

• Use of plain Option[List[A]] is not supported due to type erasure. Instead, use OptionalList[A]. There are plans to switch to shapeless to alleviate this restriction in a later version
• Use the Bytes to instruct caseconfig to parse the configuration value in bytes notation (e.g., 5 MB). Bytes is however a type alias for Long which is how TypeSafe Config represents the parsed value

import com.pellucid.caseconfig._
import com.typesafe.config.ConfigFactory

case class CacheConfig(evictionStrategy: String, maxSize: Bytes)
case class ConnectionPoolConfig(servers: List[String], maxConnections: Int, minConnections: Option[Int])
case class MyConfig(pool: ConnectionPoolConfig, cache: Option[CacheConfig], latencyPercentiles: OptionalList[Double])

val config = ConfigFactory.parseString(
        """
        |{
        |   pool = {
        |       servers = [ "web0.myapp.ninja", "web1.myapp.ninja" ]
        |       maxConnections = 12
        |   }
        |
        |   latencyPercentiles = [ 50, 75, 90, 95, 99, 99.9 ]
        |}
        """.stripMargin)

val myConfig = config.get[MyConfig]

Result:

myConfig =
    MyConfig(
        ConnectionPoolConfig(
            List(
                "web0.myapp.ninja",
                "web1.myapp.ninja"
            ),
            12,
            None
        ),
        None,
        OptionalList(
            Some(
                List(50.0, 75.0, 90.0, 95.0, 99.0, 99.9)
            )
        )
    )