Add support for OpenMetrics

[joe-elliott]

The official go and python clients already support OM and the Ruby client has a running issue tracking progress.

The Java client is in wide use and it would benefit the Prometheus ecosystem for it to also support OM.

[brian-brazil]

I'm already working on this.

[berkus]

Hmm, PR link?

[fstab]

What's missing? OpenMetrics support is available since a long time. If you don't see it, it's likely because OM format is only produced if you request with the OM HTTP header:

curl -H 'Accept: application/openmetrics-text; version=1.0.0; charset=utf-8' http://localhost:8080/metrics

[berkus]

Oh, thanks @fstab

I basically wanted to look into the java implementation, hence asked for a PR link. If you could point into the section of the code that implements openmetrics specifically that'd be helpful as well.

[fstab]

You can just search for an OpenMetrics type, like Info.

[berkus]

Thank you, will try that!