Human editable JSON-like or YAML-like program configuration in Java

Is there a Java library similar to libconfig for C++, where the config file is stored in a JSON-like format that can be edited by humans, and later read from the program?

I don't want to use Spring or any of the larger frameworks. What I'm looking for is a small, fast, self-contained library. I looked at java.util.Properties, but it doesn't seem to support hierarchical/nested config data.

Solution

I think https://github.com/typesafehub/config is exactly what you are looking for. The format is called HOCON for Human-Optimized Config Object Notation and it a super-set of JSON.

Examples of HOCON:

HOCON that is also valid JSON:

{
    "foo" : {
        "bar" : 10,
        "baz" : 12
    }
}

HOCON also supports standard properties format, so the following is valid as well:

foo.bar=10
foo.baz=12

One of the features I find very useful is inheritance, this allows you to layer configurations. For instance a library would have a reference.conf, and the application using the library would have an application.conf. The settings in the application.conf will override the defaults in reference.conf.

Standard Behavior for loading configs:

The convenience method ConfigFactory.load() loads the following (first-listed are higher priority):

system properties application.conf (all resources on classpath with this name)

application.json (all resources on classpath with this name)

application.properties (all resources on classpath with this name)

reference.conf (all resources on classpath with this name)