I am an engineer for Caucho on the Resin Application Server, and was testing JSPWiki on Resin version 4.0.34. I would like to submit 2 fixes to enable JSPWiki to run better on Resin 4:
#1. JSPWiki is calling getOutputStream after getWriter(). The servlet spec dictates we throw IllegalStateException for this situation. I see JSPWiki already has handling in UtilJ2eeCompat to use an OutputStream rather than a Writer depending on the container. The Resin check should have "useStream = true".
#2. As a consequence of #1, JSPWiki serves empty content. This is due to buffering inside the PrintWriter used by WikiJSPFilter.ByteArrayResponseWrapper. The PrintWriter is never flushed when toString() is called on ByteArrayResponseWrapper. (This may not be a Resin specific issue.)
I will attempt to attach a patch file to this bug report containing my fix to WikiJSPFilter.java.