Akka/Scala example source code file (MetricsListener.java)

This example Akka source code file (MetricsListener.java) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Akka and Scala source code examples by using tags.

All credit for the original source code belongs to akka.io; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Akka tags/keywords

actor, akka, cluster, clustermetricschanged, cpu, event, factorial, heapmemory, load, loggingadapter, metricslistener, override, untypedactor, used

The MetricsListener.java Akka example source code

package sample.cluster.factorial;

//#metrics-listener
import akka.actor.UntypedActor;
import akka.cluster.Cluster;
import akka.cluster.ClusterEvent.ClusterMetricsChanged;
import akka.cluster.ClusterEvent.CurrentClusterState;
import akka.cluster.NodeMetrics;
import akka.cluster.StandardMetrics;
import akka.cluster.StandardMetrics.HeapMemory;
import akka.cluster.StandardMetrics.Cpu;
import akka.event.Logging;
import akka.event.LoggingAdapter;

public class MetricsListener extends UntypedActor {
  LoggingAdapter log = Logging.getLogger(getContext().system(), this);

  Cluster cluster = Cluster.get(getContext().system());

  //subscribe to ClusterMetricsChanged
  @Override
  public void preStart() {
    cluster.subscribe(getSelf(), ClusterMetricsChanged.class);
  }

  //re-subscribe when restart
  @Override
  public void postStop() {
    cluster.unsubscribe(getSelf());
  }


  @Override
  public void onReceive(Object message) {
    if (message instanceof ClusterMetricsChanged) {
      ClusterMetricsChanged clusterMetrics = (ClusterMetricsChanged) message;
      for (NodeMetrics nodeMetrics : clusterMetrics.getNodeMetrics()) {
        if (nodeMetrics.address().equals(cluster.selfAddress())) {
          logHeap(nodeMetrics);
          logCpu(nodeMetrics);
        }
      }

    } else if (message instanceof CurrentClusterState) {
      // ignore

    } else {
      unhandled(message);
    }
  }

  void logHeap(NodeMetrics nodeMetrics) {
    HeapMemory heap = StandardMetrics.extractHeapMemory(nodeMetrics);
    if (heap != null) {
      log.info("Used heap: {} MB", ((double) heap.used()) / 1024 / 1024);
    }
  }

  void logCpu(NodeMetrics nodeMetrics) {
    Cpu cpu = StandardMetrics.extractCpu(nodeMetrics);
    if (cpu != null && cpu.systemLoadAverage().isDefined()) {
      log.info("Load: {} ({} processors)", cpu.systemLoadAverage().get(), 
        cpu.processors());
    }
  }

}
//#metrics-listener