How to set default list value if system variable is not in type configuration?

Question

Here is the typesafe config documentatioin.

In accordance with this, you can override the following properties:

akka { loglevel = DEBUG loglevel = ${?LOG_LEVEL} } 

So, in this case logLevel will be DEBUG or the value from the LOG_LEVEL system variable.

What about list configuration properties?

 akka { someListProperty = ["oneValue"] someListProperty = [${?LOG_LEVEL}] } 

In this case, if the system variable is missing, someListProperty will be overridden by an empty list.

How to set the default list value if there is no system variable?

Answer 1

Old question, but I had a similar problem. You can do it as follows:

 akka { defaultProperty = "oneValue" defaultProperty = ${?SYSTEM_VAR} someListProperty = [${akka.defaultProperty}] } 

Answer 2

One possible way would be to have a default configuration and use a backup for this configuration with a set of variables.

For example, this source uses a configuration override on line 58, and then line 92 changes the configuration.