I wouldn't make it
J2EE. I'd just go to sourceforge and get the HttpClient jar file, and code a little Java app that requests a page from my JBoss server. If it throws an exception, times-out, or anything bad, send an email. Whatever the case, go to sleep for X minutes then loop back and do it all again. Then you'll get to work in the morning after JBoss crashes and you'll have a mailbox full of errors!
Now, if you want to make it hands-off, you would start your Java program as a service (there are several tools that allow you to start a Java app as a service). That way, you can set it to automatic start and you won't need to worry about making sure it gets started each time the machine comes-up.
--Dale--