Metrics
Capturing JVM and application-level metrics
...The central library for Metrics is metrics-core, which provides some basic functionality. The starting point for Metrics is the MetricRegistry class, which is a collection of all the metrics for your application (or a subset of your application). Each metric is associated with a MetricRegistry, and has a unique name within that registry. A gauge is the simplest metric type. It just returns a value. If, for example, your application has a value which is maintained by a third-party library, you can easily expose it by registering a Gauge instance which returns that value.