The JSP sample is very basic and as I see is absolutely correct. The library set is also complete. So obviously something is wrong with the environment.
If you are absolutely sure there is no error messages and stack traces in both server STDOUT and STDERR logs, please try to run an offline test:
java -Xmx512m -jar pd4ml.jar
It should run PD4ML in GUI mode. Try to open an HTML and to convert it to PDF. Does it work?