Maven Multi Module benefits over simple dependency

Question

I have some years of experience with maven projects, even with multi modules ones (which has made me hate the multi modules feature of maven (so the disclaimer is now done)) and even if I really like maven there is something I cannot get a clear answer about :

What is a typical usecase of a multi module maven project ? What is the added value of such a structure compared to simple dependencies and parent pom ?

I have seen a lot of configuration of multi module projects but all of them could have clearly been addressed by creating a simple structure of dependency library living their own life as deliverables (even with a parent pom, as a separate deliverable : factorising depedencies and configuration) and I haven't found any usecase where I can clearly see an added value of the multi module structure.

I have always found that this kind of structure brings an overkilling complexity with no real benefit : where am I missing something ? (to be truly honest, I can get that some ear can benefit from this kind of structure but except from that particular usecase, any other real use and benefit ?)

Answer 1

Here's a real life case.

I have a multi-module project (and to your rant... I haven't seen any complications with it.) The end result is a webapp but I have different modules for api, impl, and webapp.

12 months after creating the project I find that I have to integrate with Amazon S3 using a stand-alone process run from a jar. I add a new module which depends on api/impl and write my code for the integration in the new module. I use the assembly plugin (or something like it) to create a runnable jar and now I have a war I can deploy in tomcat and a process I can deploy on another server. I have no web classes in my S3 integration process and I have no Amazon dependencies in my webapp but I can share all the stuff in api and impl.

3 months after that we decide to create a REST webapp. We want to do it as a separate app instead of just new URL mappings in the existing webapp. Simple. One more module, another webapp created as the result of the maven build with no special tinkering. Business logic is shared easily between webapp and rest-webapp and I can deploy them as needed.