Time based metrics will be reset after any get request

Jmx metrics can be query by http request.

But metrics will be reset after any get request.

The root cause may be the implement of Histogram's method "snapshot"

@Override
public Snapshot snapshot() {
  return histogram.snapshotAndReset();
} 

It will call snapshot and reset at the same time.

I think it should not be reset cause we may need history metrics.