Exjprop is a library for reading Java properties files from various sources.

Implementations are provided for File, Stream, Function (which returns a stream), and Amazon S3.

API documentation is available at http://hexdocs.pm/exjprop

{:exjprop, "~> 1.2"}

First, define a property loader module

defmodule MyApp.PropLoader do
  use Exjprop.Loader
  import Exjprop.Validators, only: [required: 1]

  property "endpoint.secret", {:my_app, MyApp.Endpoint, :secret_key_base}

  property "foo.bar", {:my_app, MyApp.Foo, :bar}, secret: false, pipeline: [&required/1]
  property "foo.quux", {:my_app, MyApp.Foo, :quux}, secret: false, pipeline: [&required/1, &integer/1]

  property "other_app.thing", {:other_app, :thing}, secret: false, pipeline: [&required/1, &integer/1]
end

Next, when your application starts, have it read in your properties and update your application environment

defmodule MyApp do
  use Application
  import Supervisor.Spec
  alias MyApp.PropLoader

  def start(_type, _args) do
    PropLoader.load_and_update_env({:system, "MYAPP_PROPS_FILE"})
    ...

This configuration will cause the prop loader to read the MYAPP_PROPS_FILE environment var, and attempt to use that as a uri for loading a properties file. The uri should either file:///path/to/file.properties or s3:///myapp_bucket/path/to/s3/file.properties.

To enable support for retrieving property files from S3, a few additional dependencies are required.

  {:ex_aws, "~> 2.1"},
  {:sweet_xml, "~> 0.6"},

ExAws also needs an HTTP client - it defaults to Hackney, but can be modified (see https://hexdocs.pm/ex_aws/ExAws.Request.HttpClient.html)

Enable validators for json to keyword lists or maps

  {:jason, "~> 1.1.2"},