I've been blissfully ignorant and simply putting jars into lib/ext or the app's WEB-INF/lib, but today I hit a problem trying to use Apache Tika. If I put the tika jar in lib/ext, Jetty fails to start , and I'm wondering if it's because the Tika jar has an older version of an slf4j class.
Is this something I can get around with modules? Maybe I can add the tika jar but keeps its copy of slf4j classes private to itself? I remember jboss modules doing something like this, but I don't see anything on the doc page 
(I'm using Jetty 9.2)