If you open the bin folder of the Java installation, you can find quite a few command-line utilities there that can be used to diagnose issues and monitor an application deployed with the Java Runtime Environment (JRE). They use different mechanisms to get the data they report. The mechanisms are specific to the Virtual Machine (VM) implementation, operating systems, and release. Typically, only a subset of the tools is applicable to a given issue.
In this recipe, we will focus on the diagnostic command introduced with Java 9 as a command-line utility, jcmd. If the bin folder is on the path, you can invoke it by typing jcmd on the command line. Otherwise, you have to go to the bin directory or prepend the jcmd in our examples with the full or relative (to the location of your command line window) path to the bin folder.
If you do type it and...
