What is a tool or Tomcat configuration that can notify me when my web app goes down?

I have a Java web application running on an internal company network.

I need to ensure it's always up and running. So I want to find a tool I can install on the internal network that checks it regularly and notifies me if it's down.

Alternately, is there a way to configure Tomcat to do this for me?

Also, it would be good if this tool could help me sanity test the web app's functionality. Like, perform a search like a user would and check to see if expected search results appear. That sort of thing.

What would be a good tool for this kind of thing?