Based on the popular and very usefulmod_rewritefor apache, UrlRewriteFilter is a Java Web Filter for any J2EE compliant web application server (such asResin,OrionorTomcat), which allows you to rewrite URLs before they get to your code. It is a very powerful tool just like Apache's mod_rewrite. More on the main web site.
General Tips for debugging UrlRewriteFilter:
Turn ondebug logging(see filter params in manual).
Simplifythe problem as much as possible. Perhaps make a new web application without other filters/servlets, try and replicate the problem there.
Use anHTTP debuggerto check that what you think is happening really is.
If you have more tips please comment on the DebuggingTips wiki page
If you think you have found a bug:
Read the source
Write a unit test that proves the bug, this reduce the amount of time it will take to fix the bug.