Maven and optional runtime dependencies

Question

I'm starting to fix a java project that has used maven and while I've got the project to build, at runtime it fails with missing dependencies. I've had a look and the errors are missing optional dependencies of included compile time dependencies. I can go through and add these but it seems to me that I can have everything building and running nicely only for some piece of code that I missed to use a missing dependency and the whole thing falls apart.

What I really want to know is whether there is an automated way to find optional dependencies that I have chosen to not include. I have used mvn dependency:tree but this only shows the dependencies I have (not sure of the scope it checks) and I have tried mvn dependency:analyze but this seems to show dependencies it thinks I don't use and those that have been pulled down indirectly. What I cannot see is how to see a list of optionals I don't include.

Currently my method of working around this is to read the poms and try to work it out from there, but I don't see this as particularly robust.

For reference, I am fairly new to maven style dependency management and on the face of it like it, but this optional thing is a bit of a stumbling block for me. I understand that optionals stop me pullin down dependencies I won't be using, but it hasn't clicked for me how I can workout what optionals are available and that I do need.

I am using Eclipse Juno, m2Eclipse (also have maven 3.0.5 cli), java 6/7.

Anyone got any ideas of how I can do this better, or what I am completely overlooking?

Answer 1

No the things are - somewhat - just this way. Maven does not do dependency management, it allows you to do dependency management by offering tools to use and analyze them. So the work still is on the developers side. People often mix that up.

This is mainly caused by the fact that projects often have different deployment targets. As a result sometimes they collect a bunch of jar files which are copied once into tomcat and a different set of files for weblogic. So there might be a readme in your project that states what to copy prior to deployment of the maven artifacts. Or it is implicit knowledge - then you're doomed.

dependency:analyze works on bytecode not on sources. therefore it does not see what maven knows.

Maybe mvn help:effective-pom gives a better basis to analyze the whole thing? Or you could try to modify the dependency plugin to show that information as well. Maven plugins are not so hard to work with.

I'm not aware of a plugin that displays all optional transitive dependencies. But since the pom.xml files of dependencies are downloaded into the local maven repo you could do a text search there.

A while ago there was a discussion on optional dependencies as well: Best strategy for dealing with optional dependencies - it might be helpful too.