Add public API to load configuration files

[leszko]

Add load() method to Config, ClientConfig, and ClientFailoverConfig. This method loads the config with the "known" locations. If not found, the default config is returned.

fix #16809

Related to spring-projects/spring-boot#19487

This is the completion of the initial work done by @jerrinot and opened as a draft PR: #16386, I addressed all the comments from there.

[blazember]

I like the change 👍

One improvement idea. Since this logic has become a public API now, perhaps it would make sense going forward to let the user control what happens if no config is found. Unsuccessful load attempts might indicate a deployment/environment issue that one might want to fail fast if it happens. So something like Config#load(MissingConfigFileBehavior) and

enum MissingConfigFileBehavior {
  LOAD_DEFAULT_CONFIG,
  THROW_EXCEPTION
}

with

Config#load() {
  load(LOAD_DEFAULT_CONFIG);
}

WDYT?

[leszko]

Thanks @blazember . I'll actually let you and the Core team decide on MissingConfigFileBehavior. You probably know better if people missed such a feature. If unsure, we can always add MissingConfigFileBehavior later.

[pveentjer]

Do we log which file got loaded? So that at least from the logging it is obvious which file is being used. It can be extremely annoying if you are fighting an configuration issue and then you finally determine that your file didn't get loaded in the first place.

I had that problem a few times with simulator and every time I wanted to smack my head into my desk.

[leszko]

I think that we do log it. At least I see something like this in the logs:

INFO: Loading configuration '/opt/hazelcast/hazelcast.yaml' from System property 'hazelcast.config'

[pveentjer]

I like the change +1

One improvement idea. Since this logic has become a public API now, perhaps it would make sense going forward to let the user control what happens if no config is found. Unsuccessful load attempts might indicate a deployment/environment issue that one might want to fail fast if it happens. So something like Config#load(MissingConfigFileBehavior) and

enum MissingConfigFileBehavior {
  LOAD_DEFAULT_CONFIG,
  THROW_EXCEPTION
}

with

Config#load() {
  load(LOAD_DEFAULT_CONFIG);
}

WDYT?

Perhaps it is simplest to return null or an exception instead of adding a strategy? KISS

null can be checked and exception can be caught; especially when properly documented.

[leszko]

verify