Here's a simple JSP to list out all the JVM environment keys and values. Very simple, but occasionally useful. For example, a few weeks ago I needed to see which SSL keystore (javax.net.ssl.trustStore) our test servers were using.
I'm sure every Java developer has written similar code at some point, so I won't claim it's original, unique, or ingenious. But if you find it useful, go ahead and use it instead of writing another.