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@Path("ping")
public class PingResource {

    @GET
    @Counted(monotonic = true)
    public String ping() {
        return "Enjoy MicroProfile and Java EE 8";
    }

    @Gauge(unit = "correctness")
    public int answer() {
        return 42;
    }
}

According to the microprofile specification, the @Counted annotation:

"Denotes a counter, which counts the invocations of the annotated object."

In contrary, the @Gauge annotation:

"Denotes a gauge, which samples the value of the annotated object."

Typical output (curl -H"Accept: application/json" http://localhost:9080/metrics/application):

    {
        "com.airhacks.ping.boundary.PingResource.answer":42,
        "com.airhacks.ping.boundary.PingResource.ping":1
}  

The @Counted annotation automatically counts the total invocations of the annotation method (monotonic=true), or the amount of parallel invoked methods at any time: (monotonic=false) (ConcurrentGauge will probably replace: (monotonic=false)).

On the other hand, the @Gauge exposes the return value of the annotated method as a metric.

@Gauge annotations are used to expose metrics with dedicated methods. The values have to be provided by the developer (e.g. number of orders in the DB) and the method is going to be invoked by the metrics infrastructure.

See you at Web, MicroProfile and Java EE Workshops at Munich Airport, Terminal 2 or Virtual Dedicated Workshops / consulting. Is Munich's airport too far? Learn from home: airhacks.io.