In my Maven build, I use exec-maven-plugin to run an external tool for Java code generation. In this case the flatbuffers compiler (flatc).

By default, flatc always runs, so you always get a new .java file. This will always trigger Java compiler to run, which will in turn always trigger jar packaging to run, etc. I would like flatc to only run if it’s source file is updated, so I can get a properly incremental build and avoid needlessly recompiling.