Programmers' Pain

Things you shouldn’t do #2: Hack around maven-shade-plugin limitations

Shutter Shades make everyone Look like a Douche ( maven-shade-plugin is a handy plugin which allows you to collect all of your project dependencies - incl. transitive dependencies - and put everything together into a single, shaded jar file. I use this plugin to deliver a Java application as a single jar file containing all needed resources to simplify the application launch descriptor. But sometimes you have more than one Maven project that you want to deliver as a single jar file. And sometimes you even have a parent Maven project that contains a list of dependencies and for each of them you want to create a single jar file. This kind of project setup might lead you to the idea to call the maven-shade-plugin (multiple times) directly from command line to create your jar files which will end up with the follow error message: "You have invoked the goal directly from the command line. This is not supported. Please add the goal to the default lifecycle via an element in your POM and use "mvn package" to have it run.". If you still want to use the plugin and if you're not afraid of bloody hacks than continue reading - otherwise you have to accept this limitation since it's there for a good reason 🙂


maven-duplicate-finder-plugin: find duplicate classes in maven artefacts

Lately I was looking for a Maven plugin to solve the problem that I want a certain Maven build to fail as soon as new duplicate classes have been introduced by other developers / third party dependencies while knowing that I already have some duplicate classes that I can't get rid of right now. Basically a duplicate classes detector with the possibility to define an exclude list - that's where the maven-duplicatefinder-plugin of Ning Inc. will give you a helping hand.


maven-jarsigner-plugin: sign multiple jar files

Image from the Nuvola icon theme for KDE 3.x by David Vignoni Source: (LGPL)

The maven-jarsigner-plugin is a pretty handy Maven plugin if you want to sign the jar file produced by your Maven artefact build. The plugins documentation does provide several examples for that use case.

But if you want to sign just some jar files in the scope of your Maven build - especially if you need to apply certain include / exclude patterns - than the documentation provides only the configuration options you have to put together to make it work. Here's an example how to sign several jar files using include / exclude patterns.


Things you shouldn’t do #1: Recursive Maven Builds

Recursion - You gotta know when to stopToday I've found a new way to kill the resources of my development PC via doing recursive Maven builds. Yes, recursive! Why? Because I can and it's fun! It started with an pretty old part of a Maven build which used Python scripts to compile Java classes outside of the Maven artefact scope. Those classes are than used to launch a little helper JVM which resolves the used annotations of a class you've passed to stdin and prints the annotations class name to stdout. You know, the usual stuff you do in case the used Java decompiler doesn't support Java annotations. It all started with a Maven project which did call a Python script...