JConsole

JConsole is a graphical monitoring tool using the JMX specification to provide information about the performance and resource consumption of the JVM. It is bundled with a JDK.

The main information to check in JConsole is the memory consumption and memory pools.

jconsole display of memory usage

The bar chart on the lower right-hand side shows the memory consumed by the memory pools in heap and non-heap memory. The bar turns red when the memory used exceeds the memory usage threshold.

For more information, see http://docs.oracle.com/javase/8/docs/technotes/guides/management/jconsole.html.