SpanSamplingDemo.java

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package org.apache.hc.client5.http.observation.example;

import java.net.URI;
import java.util.EnumSet;

import io.micrometer.core.instrument.Counter;
import io.micrometer.core.instrument.Metrics;
import io.micrometer.observation.ObservationRegistry;
import io.micrometer.prometheusmetrics.PrometheusConfig;
import io.micrometer.prometheusmetrics.PrometheusMeterRegistry;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.client5.http.observation.HttpClientObservationSupport;
import org.apache.hc.client5.http.observation.MetricConfig;
import org.apache.hc.client5.http.observation.ObservingOptions;
import org.apache.hc.core5.http.ClassicHttpResponse;
import org.apache.hc.core5.http.io.support.ClassicRequestBuilder;

public final class SpanSamplingDemo {

    private static final URI URL_OK = URI.create("https://httpbin.org/get");
    private static final URI URL_SKIP = URI.create("https://httpbin.org/anything/deny");

    public static void main(final String[] args) throws Exception {
        final PrometheusMeterRegistry reg = new PrometheusMeterRegistry(PrometheusConfig.DEFAULT);
        Metrics.addRegistry(reg);

        final ObservationRegistry obs = ObservationRegistry.create();
        final MetricConfig mc = MetricConfig.builder().build();

        final ObservingOptions opts = ObservingOptions.builder()
                .metrics(EnumSet.of(ObservingOptions.MetricSet.BASIC, ObservingOptions.MetricSet.IO))
                .tagLevel(ObservingOptions.TagLevel.LOW)
                .spanSampling(uri -> {
                    // Skip any URI containing "/deny"
                    return uri == null || !uri.contains("/deny");
                })
                .build();

        final HttpClientBuilder b = HttpClients.custom();
        HttpClientObservationSupport.enable(b, obs, reg, opts, mc);

        try (final CloseableHttpClient client = b.build()) {
            final ClassicHttpResponse r1 = client.executeOpen(null, ClassicRequestBuilder.get(URL_OK).build(), null);
            r1.close();
            final ClassicHttpResponse r2 = client.executeOpen(null, ClassicRequestBuilder.get(URL_SKIP).build(), null);
            r2.close();
        }

        // Sum all response counters (only the first request should contribute)
        double total = 0.0;
        for (final Counter c : reg.find("http.client.response").counters()) {
            total += c.count();
        }

        System.out.println("Total http.client.response count (expected ~1.0) = " + total);
        System.out.println("--- scrape ---");
        System.out.println(reg.scrape());
    }

    private SpanSamplingDemo() {
    }
}