How to reference .properties value on application.conf

Question

I have an J2EE app which uses a custom actor system and I need to externalize some custom configurations.

Is there a way to do this? Since the application.conf is always on the classpath is there anyway I can load an external custom.properties file and use it like below

ActorSystem.akka.remote.netty.hostname = "${custom.ip}"
ActorSystem.akka.remote.netty.port = "${custom.port}"

Answer 1

I am not entirely sure what your constraints are, but in principle you have several options:

1. You can provide hardcoded configuration to your actor system, when you create it, like this:

   Map configMap = new HashMap();
   configMap.put("akka.remote.netty.hostname", custom.ip);
   configMap.put("akka.remote.netty.port", custom.port);
   
   Config config = ConfigFactory.parseMap(configMap).withFallback(ConfigFactory.load());
   ActorSystem system = ActorSystem.create("ActorSystem", config);
   

2. you can load you custom config file instead of application.conf either through code: ConfigFactory.load("custom.conf") or by setting a system property -Dconfig.resource=custom.conf and include application.conf in your custom.conf, like this:

   include "application"
   akka.remote.netty.hostname = "custom-ip"
   akka.remote.netty.port = "custom-port"
   

3. You could also provide the custom-port and ip through system properties and use defaults, if they are not defined. In that case the application.conf would look like this:

   akka.remote.netty.hostname = "default-ip"
   akka.remote.netty.port = "default-port"
   akka.remote.netty.hostname = "${?custom.ip}"
   akka.remote.netty.port = "${?custom.port}"
   

4. Or you can include custom.properties in your application.conf file. If the custom.properties does not exist if will silently be ignored. application.conf:

   akka.remote.netty.hostname = "default-ip"
   akka.remote.netty.port = "default-port"
   include "custom"
   

   custom.properties:

   akka.remote.netty.hostname = "custom-ip"
   akka.remote.netty.port = "custom-port"