The Resin team has  implemented a PHP 5 engine in JAVA! Quercus is Caucho Technology's fast, open-source, 100% Java implementation of the PHP language.

"Quercus is Caucho Technology's fast, open-source, 100% Java implementation of the PHP language. Quercus is a feature of Caucho Technology's Resin Application Server and is built into Resin - there is no additional download/install. Developers using Resin can launch PHP projects without having to install the standard PHP interpreter (http://www.php.net) as Quercus takes on the role of the PHP engine."

Joomla! is supported right out the box
Joomla%201.0.11">http://www.caucho.com/resin-3.1/doc/quercus-list-of-applications.xtpJoomla%201.0.11

Benefits:

"Quercus and Quercus' PHP libraries are written entirely in Java, thereby taking the advantages of Java applications and infusing them into PHP. PHP applications running on Quercus are simply faster, easier to develop, more capable, more secure, and more scalable than any other PHP solution.
Performance - simply faster, Development - fast, safe, and easy,  Capability - powerful Java technologies at the developer's fingertips, Security - no more pesky C memory bugs,  Scalability - PHP for the masses, literally"

In fact the PHP code is translated into servlets and then compiled into java bytecode on the first run. So it should be quite fast and best of th best, I can use my java profiling tools and library :-)
http://www.caucho.com/resin-3.1/doc/quercus.xtp