Java tools to know what my application is doing

Two critical factors are directly linked to performance when you take an application as a black box:

• Memory usage: If too much memory is consumed, it can slow down the application or even make it dysfunctional
• CPU time: If an operation is too slow, it will consume a lot of CPU cycles and impact the overall performance

Without too much external tooling (except the Java Development Kit (JDK) and/or operating system tools), you can easily extract a lot of information and start working on the performance.