Jar File Security

Ok, so let's say I have a JAR file with important info in it. What can I do to stop this file from being downloaded and read, while still being able to use it in my site?

EDIT: Using proGuard, and I think its working, not sure. If someone has a better solution tell me.

Proguard will do a good job obfuscating your code, which makes it very difficult to read and interpret. If you are worried about folks 'decompiling' to read and reuse your code obfuscation is a good tool. To convince yourself though, I'd suggest getting a decompiler and playing with it yourself, looking at your code before and after using proguard to see the results, they can be pretty dramatic and not code that I'd personally think is worth the time to 'de-obfuscate'.