Using Maven shade plugin in a multi module project - NullPointerException

Question

I have a scenario where-in I need to create an uber jar of a multi module maven project including all modules and their dependencies. I tried using maven shade plugin. but it seems to work only when I use it at the module level. If I add the plugin entry in parent pom then the build breaks (it tries to shade the parent pom)

 [INFO] Replacing original artifact with shaded artifact.
[INFO] Replacing null with C:\Projects\foo.bar\target\foobar-0.0.1-SNAPSHOT-shaded.pom
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Error creating shaded jar: null: NullPointerException -> [Help 1]

It does seem to make sense since the <packaging> for the parent maven project is pom. But there should be some way to create an uber jar for a multi module project... Any ideas people???

Answer 1

You should not be using your parent project's POM file to attempt shading; you should be using a separate aggregator project for this. Parent maven projects are used for inheritance while aggregator projects are used to perform aggregate functions over a group of sub-projects; like shading their JARs together into a uber jar. This project would simply be a pom file at the root directory of your project (the same level as all the sub-modules' folders) which references the sub-projects and has the shade plugin configuration. Make sure the packaing specified for this pom is JAR.

Here is the documentation explaining POM relationships and difference between Aggregation and Inheritance.