How to check heap usage of a running JVM from the command line?

Can I check heap usage of a running JVM from the commandline, I mean the actual usage rather than the max amount allocated with Xmx.

I need it to be commandline because I don’t have access to a windowing environment, and I want script based on the value , the application is running in Jetty Application server

Answer

You can use jstat, like :

 jstat -gc pid

Full docs here : http://docs.oracle.com/javase/7/docs/technotes/tools/share/jstat.html