Micrometer's equivalent of Prometheus' labels
Further digging showed that only the keys of micrometer tags have to be predeclared - but the constructor really takes pairs of key/values; the values don't matter. And the keys have to be specified when using the metric.
This works:
private static final String COUNTER_BATCHMANAGER_SENT_REQUESTS = "batchmanager.sent.requests";
private static final String METHOD_TAG = "method";
private static final String PATH_TAG = "path";
private final Counter requestCounter;
...
requestCounter = Counter.builder(COUNTER_BATCHMANAGER_SENT_REQUESTS)
.description("Total number of rest requests sent")
.tags(METHOD_TAG, "", PATH_TAG, "")
.register(meterRegistry);
...
Metrics.counter(COUNTER_BATCHMANAGER_SENT_REQUESTS, METHOD_TAG, methodName, PATH_TAG, path)
.increment();