public ByteBuffer writeBody(ByteBuffer buffer) {
        buffer.putInt(metricValueMap.size());
        for (Map.Entry<Byte, Double> entry : metricValueMap.entrySet()) {
            buffer.put(entry.getKey());
            buffer.putDouble(entry.getValue());
        }
        return buffer;
    }
@return the broker id who reported this metric.
core/src/main/java/kafka/autobalancer/metricsreporter/metric/AutoBalancerMetrics.java