There is a little choice between the codecoverage tools with seamless integration to maven.
Atlassian Clover is probably cool, but it's paid, so I don't consider it in this project
Cobertura is dead, though still serves its purpose.
JaCoCo is the most popular actively maintained alternative
But I find that PIT is really cool. It not only provides the code coverage, it also tests how good are your tests. Running time is much longer than for usual test suite but it does make a lot of sense.
Add the codecoverage tool