Currently I’m doing deployment tests and proof-of-concept tests for various technologies (RMI, Session Bean, JNDI, JSF, Seam, Web Services, Spring, Hibernate, .etc.) on different application servers (JBoss, IBM WebSphere, SAP Netweaver). Some of the app servers are only certified or supported with Java5. So I frequently ran into problems resulting from having classes around compiled for Java6. I was already thinking of writing a tool that could analyze a Jar or class file and get its version information. But luckily I found a tool ready to do the job.