in src/main/java/org/apache/rocketmq/exporter/collector/RMQMetricsCollector.java [279:288]
private static <T extends Number> void loadGroupDiffMetric(GaugeMetricFamily family, Map.Entry<ConsumerTopicDiffMetric, T> entry) {
family.addMetric(
Arrays.asList(
entry.getKey().getGroup(),
entry.getKey().getTopic(),
entry.getKey().getCountOfOnlineConsumers(),
entry.getKey().getMsgModel()
),
entry.getValue().doubleValue());
}