BOM override order (with overlapping BOMs)

Question

I have a parent POM and a normal Maven project.

Both define BOMs in their dependencyManagement. In some cases, these BOMs may overlap, e.g. both specify a version for log4j.

From my tests it seems that:

• For overlapping BOMs in the parent POM, the first one wins, i.e. supplies the version for the artifact.
• If a BOM from the child and from the parent overlap, then the version from the BOM in the child wins.

Unfortunately, I did not find any documentation about this.

Am I right and can I rely on this behaviour?

Answer 1

Logging framework traditionally lives "next to" your actual code, so it is a bit unclear how to handle this.

I found that separating the build phase dependencies from the deployment phase dependencies works for me.

The basic idea is that you write the code only requiring a dependency to the API of the logging framework (slf4j used to be a natural choice), and then you have several deployment Maven configurations (one for JBoss, one for WebSphere, one for running in your IDE etc) where you add the dependencies relevant to that deployment.

So my suggestion is to change your codebase accordingly to only have API dependencies for the logging framework, and then create a new Maven project for each actual deployment type. You might also want to bake in deployment specific configuration files if needed.