Website blocking

You mean block it from being accessed by your PC? And why Java?

Normally you just need to use a firewall, either one locally installed on your PC or at the router (it may even be part of a parental control feature).

You need to be more specific wrt intent because simply asking to block a website w/ Java is far too vague (well, unless you want an equally vague response).

You'd typically need something that allows deep inspection of the network traffic. I know some of the enterprise grade IDS / IPS appliances will do this. I know it can be done with the IBM Proventia series of inline appliances, and possibly others such as Cisco IPS series or CheckPoint.

I should probably note that a lot of this maybe cost prohibitive for a home user.