Check Java Thread CPU Usage

Today I came across a question: if an application occupies 100% CPU time, and its source code is extremely large so that reading its source code to find what is going on may not be an option; what should we do to find out the problem?

Let's assume the application is written in Java.

First, we can use jstack combined with jps to print out threads' stack trace, which gives us a good idea about which methods are being executed.

We can also use jconsole with some plugin to display threads' CPU usage. The jconsole plugin is based on JTop (/demo/management/JTop).