For a customer we need to generate detailed test reports for integration tests which not only show, that everything is green, but also what the test did. My colleagues and I
Have you looked at Maven Sure-fire reports?
You can generate a HTML report from your JUnit Tests.
http://maven.apache.org/plugins/maven-surefire-report-plugin/
I'm not sure how customizable it is though. But it's a good starting point.
I also know that TestNG ( alternative to JUnit ) has some report generating capabilities. http://testng.org/doc/documentation-main.html#logging-junitreports
I would also recommend log4j http://logging.apache.org/log4j/1.2/manual.html