Nano-library which provides the ability to define typesafe (!) Configuration templates for applications.

A Configuration is a set of named and typed Property instances, which are defined using a ConfigurationTemplate. Each defined Property can be set with a default value, or be blank with a requirement to be overridden. At runtime, the template is reified into a concrete Configuration object, but if any properties are missing this process will throw a Misconfiguration error.

Assuming that the reification process is successful, property values can be retrieved in an (actually) type-safe manner, and are applied in the following descending order of precedence:

1. JVM system property
2. Named environment property
3. Default value

This is from the Kotlin version, but the Scala and Java APIs are broadly the same:

// simple typed values
val USER = Property.string("USER")
val AGE = Property.int("AGE")

// provide custom mapping functions to convert from strings to domain
val PATIENCE_LEVEL = Property("DURATION", { i: String -> Duration.parse(i) }, { it.describe() })

// build your template
val configTemplate = ConfigurationTemplate()
      .requiring(USER) // will be supplied by the environment
      .withProp(AGE, 2) // falls back to a default typed value
      .withProp(PATIENCE_LEVEL, Duration(10)) // custom typed property with default

// attempting to build a configuration with missing values will fail with a Misconfiguration exception
val config = configTemplate.reify()

// retrieval of values in a typesafe way
val patience: Duration = config.valueOf[PATIENCE_LEVEL]

Currently, the library is published in Java, Kotlin and Scala versions in JCenter (and synced to Maven Central).

Java:

<dependency>
  <groupId>io.github.daviddenton</groupId>
  <artifactId>configur8</artifactId>
  <version>1.7.0</version>
</dependency>

Kotlin:

<dependency>
  <groupId>io.github.daviddenton</groupId>
  <artifactId>konfigur8</artifactId>
  <version>1.7.0</version>
</dependency>

libraryDependencies += "io.github.daviddenton" %% "configur8" % "1.7.0"

See the example code in scala or java or kotlin