Health Probe for frozen server.

A "hung" serve is perhaps too general a description, and you need to find out exactly what made the server hang and in what way. For existing requests might be taking a long time to process, the OS might still be responsive, and the jvm might still be taking new incoming requests but was just not able to process them, in which case a TCP Half Open monitor would not be effective if not making things worse.

You can just create a simple HTTP monitor modeled after a generic one, using a rare random string, e.g. "/xkxjskdlskfdjgf" as the request path; if you get an error response, most likely "404 Not Found", then the jvm Webserver is working. Bear in mind that this monitor only checks if your webserver is processing an http request, not if your java application is actually working. For that you should really ask the app admin to provide a URL with defined output for use in your monitor.