I want to create an application with Java EE on a JONAS server for monitoring other applications and servers created with Java EE and C++.
So I'm looking for an API or something to help me.
How about using Java Management Extensions (JMX)? See a brief description here.
BTW there are quite a lot of tools (e.g., JConsole by default in every JDK), are you sure you have to create a new monitor? I do not know your specific needs, but maybe you can use some existing tool for the job.