How to find unneccesary dependencies in a maven multi-project?

Question

If you are developing a large evolving multi module maven project it seems inevitable that there are some dependencies given in the poms that are unneccesary, since they are

Answer 1

When you have A -> B, B -> C, and then refactor such that A -> (B, C). IF it is the case that A still compiles against B, you very much don't want to simply pick up the dependency because you receive it transitively.

Think of the case when A -> (B-1.0, C-1.0), B-1.0 -> C-1.0. Everything's in sync, so to avoid "duplication" you remove C from A's dependency. Then you upgrade A to use B-2.0 -> C-2.0. You begin to see errors because A wants C-1.0 classes but found C-2.0 classes. While quickly reconcilable in this scenario, it is far less so when you have lots of dependencies.

You very much want the information in A's pom that says that it explicitly expects to find C-1.0 on the classpath so that you can understand when you have transitive dependency conflicts. Again, Maven will do the job of ensuring that the "closest" version of any particular jar ends up on your classpath. But when things go wrong - you want all the dependency metatdata you can get.

On a slightly more practical note, a dependency is unused when you can remove it from your pom and all of your unit/integration/acceptance tests still pass. ;-)