Micrometer with Dynamic Tags

 With Micrometer, it is easy to create a counter with Builder:

Counter okCounter = Counter.builder("http.status.count")
        .tag("status", "200")
        .description("The number of OK count")
        .register(meterRegistry);

Counter notFoundCounter = Counter.builder("http.status.count")
        .tag("status", "404")
        .description("The number of not found count")
        .register(meterRegistry);

However, it is not feasible to create counter for every HTTP status.  We can use Java HashMap to cache the creation dynamically by leveraging the method computeIfAbsent

import io.micrometer.core.instrument.Counter;
import io.micrometer.core.instrument.MeterRegistry;
import java.util.concurrent.ConcurrentHashMap;
import java.util.Map;
import org.springframework.http.HttpStatus;

public class HttpStatusCounter {
    private static final String HTTP_STATUS_COUNT = "http.status.count";
    private final MeterRegistry meterRegistry;
    private Map<Integer, Counter> httpStatusCounterMap;

    public HttpStatusCounter(MeterRegistry meterRegistry) {
        httpStatusCounterMap = new ConcurrentHashMap<>();
        this.meterRegistry = meterRegistry;
    }

    public void increment(HttpStatus status, int amount) {
        Counter statusCounter = httpStatusCounterMap.computeIfAbsent(
                status.value(), k -> Counter.builder(HTTP_STATUS_COUNT)
                        .tag("status", String.valueOf(status.value()))
                        .register(meterRegistry));
        statusCounter.increment(amount);
    }
}