Auto-compiling javaflow
Just yesterday I managed to commit what I actually wanted to have ready for the ApacheCon (well!). Cocoon trunk now features an auto-compiling javaflow implementation. Java source files are being transparently compiled and instrumented for continuation-based flow execution. It probably still needs some polishing but this new version should give you almost the same try-and-error roundtrip as the javascript based flow. There are quite some things (besides the bytecode level work) left to do. So I hope some volunteers will chime in.
Update: javaflow and the the auto-compilation are factored out as separate jars and therefor can easily be integrated in other projects as well