How to use org.apache.druid.java.util.metrics

 @Override
 public ScheduledExecutors.Signal call()
 {
  // Run one more time even if the monitor was removed, in case there's some extra data to flush
  if (monitor.monitor(emitter) && hasMonitor(monitor)) {
   return ScheduledExecutors.Signal.REPEAT;
  } else {
   removeMonitor(monitor);
   return ScheduledExecutors.Signal.STOP;
  }
 }
}

@Override
public boolean doMonitor(ServiceEmitter emitter)
{
 emitJvmMemMetrics(emitter);
 emitDirectMemMetrics(emitter);
 emitGcMetrics(emitter);
 emitThreadAllocationMetrics(emitter);
 return true;
}

@Override
public boolean doMonitor(ServiceEmitter emitter)
{
 for (Stats stats : statsList) {
  stats.emit(emitter);
 }
 return true;
}

@Test
public void testDefaultFeed()
{
 StubServiceEmitter emitter = new StubServiceEmitter("dev/monitor-test", "localhost:0000");
 Monitor m = Monitors.createCompoundJvmMonitor(ImmutableMap.of());
 m.start();
 m.monitor(emitter);
 m.stop();
 checkEvents(emitter.getEvents(), "metrics");
}

private void emitThreadAllocationMetrics(ServiceEmitter emitter)
{
 final ServiceMetricEvent.Builder builder = builder();
 MonitorUtils.addDimensionsToBuilder(builder, dimensions);
 if (collector != null) {
  long delta = collector.calculateDelta();
  emitter.emit(builder.build("jvm/heapAlloc/bytes", delta));
 }
}

@Override
public boolean monitor(final ServiceEmitter emitter)
{
 return shouldReschedule(Lists.transform(monitors, monitor -> monitor.monitor(emitter)));
}

 @Override
 public void doMonitor(ServiceEmitter emitter)
 {
  monitor.doMonitor(emitter);
 }
}

public JvmMonitor(Map<String, String[]> dimensions, String feed, PidDiscoverer pidDiscoverer)
{
 super(feed);
 Preconditions.checkNotNull(dimensions);
 this.dimensions = ImmutableMap.copyOf(dimensions);
 this.pid = Preconditions.checkNotNull(pidDiscoverer).getPid();
 this.collector = AllocationMetricCollectors.getAllocationMetricCollector();
}

 @Override
 public long getPid()
 {
  return SigarUtil.getCurrentProcessId();
 }
}

@Override
public void stop()
{
 for (Monitor monitor : monitors) {
  monitor.stop();
 }
}

@Override
public void start()
{
 for (Monitor monitor : monitors) {
  monitor.start();
 }
}

public JvmMonitor(Map<String, String[]> dimensions, String feed)
{
 this(dimensions, feed, JvmPidDiscoverer.instance());
}

/**
 * Creates a JVM monitor, configured with the given dimensions, that gathers all currently available JVM-wide
 * monitors. Emitted events have default feed {@link FeedDefiningMonitor#DEFAULT_METRICS_FEED}
 * See: {@link Monitors#createCompoundJvmMonitor(Map, String)}
 *
 * @param dimensions common dimensions to configure the JVM monitor with
 *
 * @return a universally useful JVM-wide monitor
 */
public static Monitor createCompoundJvmMonitor(Map<String, String[]> dimensions)
{
 return createCompoundJvmMonitor(dimensions, FeedDefiningMonitor.DEFAULT_METRICS_FEED);
}

public HttpPostEmitterMonitor(
  String feed,
  HttpPostEmitter httpPostEmitter,
  ImmutableMap<String, String> extraDimensions
)
{
 super(feed);
 this.httpPostEmitter = httpPostEmitter;
 this.extraDimensions = extraDimensions;
 this.builder = builder();
}

 void emit(ServiceEmitter emitter, Map<String, String[]> dimensions)
 {
  for (GcGeneration generation : generations) {
   generation.emit(emitter, dimensions);
  }
 }
}

private void emitGcMetrics(ServiceEmitter emitter)
{
 gcCounters.emit(emitter, dimensions);
}

boolean gcSeen()
{
 return oldGcSeen() || youngGcSeen();
}

@Test
public void testSetFeed()
{
 String feed = "testFeed";
 StubServiceEmitter emitter = new StubServiceEmitter("dev/monitor-test", "localhost:0000");
 Monitor m = Monitors.createCompoundJvmMonitor(ImmutableMap.of(), feed);
 m.start();
 m.monitor(emitter);
 m.stop();
 checkEvents(emitter.getEvents(), feed);
}

@Override
public boolean monitor(ServiceEmitter emitter)
{
 if (started) {
  return doMonitor(emitter);
 }
 return false;
}

 @Override
 public boolean doMonitor(ServiceEmitter serviceEmitter)
 {
  return delegate.doMonitor(serviceEmitter);
 }
}