Java

<dependency>
    <groupId>io.prometheus</groupId>
    <artifactId>prometheus-metrics-core</artifactId>
    <version>1.3.6</version>
</dependency>
<dependency>
    <groupId>io.prometheus</groupId>
    <artifactId>prometheus-metrics-instrumentation-jvm</artifactId>
    <version>1.3.6</version>
</dependency>
<dependency>
    <groupId>io.prometheus</groupId>
    <artifactId>prometheus-metrics-exporter-httpserver</artifactId>
    <version>1.3.6</version>
</dependency>

implementation 'io.prometheus:prometheus-metrics-core:1.3.6'
implementation 'io.prometheus:prometheus-metrics-instrumentation-jvm:1.3.6'
implementation 'io.prometheus:prometheus-metrics-exporter-httpserver:1.3.6'

import io.prometheus.metrics.core.metrics.Counter;
import io.prometheus.metrics.exporter.httpserver.HTTPServer;
import io.prometheus.metrics.instrumentation.jvm.JvmMetrics;

public class App {

    static final Counter emailsSent = Counter.builder()
        .name("emails_sent_total")
        .help("Total number of emails sent")
        .labelNames("status")
        .register();

    public static void main(String[] args) throws Exception {
        // Register out-of-the-box JVM metrics (memory, GC, threads, classloader, etc.)
        JvmMetrics.builder().register();

        // Start the metrics HTTP server on port 9090
        HTTPServer.builder()
            .port(9090)
            .buildAndStart();

        // Increment your custom metric anywhere in your code
        emailsSent.labelValues("success").inc();
    }
}

{
    "metrics": {
        "endpoint": "/metrics",
        "interval": 15,
        "port": 9090
    }
}