What follows is lessons learned migrating to the potentially magnificent Maven2 for dependency management.

Put provided on Tomcat shared resources in your pom.xml

If you deploy jars as a shared resource on Tomcat (i.e. put the jars in common/lib) then be sure to add the provided to those dependencies in your project’s pom.xml. Otherwise, you’ll get absolutely daft class-cast errors on shared resources like:

2007-10-21 12:42:19,425 ERROR 0-SNAPSHOT] - Servlet /myExample2-1.0-SNAPSHOT threw load() exception java.lang.ClassCastException: org.apache.jackrabbit.core.jndi.BindableRepository cannot be cast to org.apache.jackrabbit.core.jndi.BindableRepository

Hahahahahahaha I think I want to kill myself. The problem is that Tomcat’s shared libraries are loaded by a different classloader than your web-app’s shared libraries (which is nice in a way, because it means you can use different versions of log4j or whatever).

So the lesson here is: Anything you want created by Tomcat and loaded by name (e.g. “jcr/repository”), be sure to exclude from your WEB-INF/lib when you deploy.

You can load the same shared resource by name for all apps

Deploying a Maven2-enabled app using Codehaus Mojo is a breeze… unless you want to deploy a context with it. And a context is the only way to load up named shared resources like a Jackrabbit repository. The solution?

$TOMCAT_HOME/conf/Catalina/$HOSTNAME/context.xml.shared

The contents are loaded for all contexts. Brilliant.

Class blahblah violates loader constraints

Oh no. This was awful. For me it was:

2007-10-21 13:16:26,331 ERROR 0-SNAPSHOT] - Exception starting filter DataServlet java.lang.LinkageError: Class org/slf4j/ILoggerFactory violates loader constraints

I needed to scour the dependencies that Maven was loading into my webapp automatically and explicitly label them as provided.