The remote-method-guesser repository contains two example servers that can be used to practice Java RMI enumeration and attacks.
The rmg-example-server exposes regular RMI services that can be enumerated and exploited using remote-method-guesser.
The rmg-ssrf-server exposes an HTTP service that is vulnerable to SSRF attacks and runs RMI services that are only
listening on localhost. This can be used to practice with remote-method-guesser's --ssrf and --ssrf-response options.
Both servers are available as containers within the GitHub Container Registry: