Paolo Antinori just published a very nice blog post explaining how he used Byteman to trace execution inside a JBoss Fuse/Karaf -based application.
The blog includes a screencast which shows him running up the app, installing the Byteman agent and loading up some trace rules. The app immediately starts printing output, showing requests being processed.
[exercise for those new to Byteman -- work out how you can use the bmsubmit command to uninstall the rules and then watch the trace disappear].
Paolo also explains how you set up your environment to reference the Byteman download and how to configure OSGi to make sure that the injected code can reference the needed Byteman agent classes.
Many thanks, Paolo!