An example tool that uses acme4j, and a good starting point to find out how acme4j is used.
This tool registers a new account with the Let’s Encrypt staging server, and fetches a certificate for a set of domains.
Run the org.shredzone.acme4j.ClientTest class with the domains to be registered as parameters.
You can also invoke the example tool via maven:
mvn exec:java -Dexec.args="example.com example.org"
Or just have a look at the source code.