To enable javac warnings I had to make it fork a javac process (and update the plugin version). I left it since the pre-existing maxmem setting apparently doesn't have effect unless javac is forked. It would be reasonable to remove this and maxmem, and then tell people they have to set MAVEN_OPTS if compilation needs a lot of memory. But hey forking seemed fine too; it isolates the compile process from Maven's JDK and classpath.