Sometimes, during development I get:
[http-8080-6] WARN org.apache.struts.action.RequestProcessor - Unhandled Exception thrown:"...
from struts.
When it reproduces, I'm debugging it and find the problem, however, If I cannot reproduce, I will never know which bugs are hiding in my application.
Is there any way to tell struts to run in debug mode or something, so that it will always show the full stack trace for the exception?
Your best bet is to configure a global exception handler. If you need substantially different handling, implement an ExceptionCatcher or ExceptionHandler. In S1.2 it's similar, but you'd override processException in a custom request processor.
(It's always best to indicate what version you're using--S1.2 and S1.3 request processors are different.)