A few weeks ago VMware internally released a best practices guide for running Java in Virtual Machines on ESX (pdf download).  Recently it was posted on the VMware Support Technical Papers portal.  This document covers subjects like:

• Multi-tiered Java Applications
• Java Heap and Virtual Machine Memory
• Virtual CPUs and Threads
• Disk I/O
• Timekeeping and
• Micro-Benchmarks

Also check out the VROOM! post discuss how ESX Runs Java Virtual Machines with Near-Native Performance.