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Micrometer Plugin

This plugin allows reporting metrics using Micrometer.

Getting Started

The Micrometer plugin is available on Maven Central as a separate artifact, but in order to use the plugin an additional library for reporting to a specific monitoring system is required. In the following description, an example is given to report to Prometheus. Thus, add the following dependencies:

<dependency>
    <groupId>io.javalin</groupId>
    <artifactId>javalin-micrometer</artifactId>
    <version>5.3.2</version>
</dependency>
<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-registry-prometheus</artifactId>
    <version>${io.micrometer.version}</version>
</dependency>

Create a registry, register the plugin, and provide a route:

public static void main(String[] args) {
    PrometheusMeterRegistry registry = new PrometheusMeterRegistry(PrometheusConfig.DEFAULT);

    MicrometerPlugin micrometerPlugin = MicrometerPlugin.Companion.create(micrometerConfig -> micrometerConfig.registry = registry);

    Javalin app = Javalin.create(config -> {
        config.plugins.register(micrometerPlugin);
    }).start(8080);

    app.get("/prometheus", ctx -> ctx.contentType(TextFormat.CONTENT_TYPE_004).result(registry.scrape()));
}

With this setup, Javalin will report several Jetty-related metrics (for example accessed endpoints and returned status codes) at the specified endpoint, suitable for being ingested by Prometheus.

Provided Metrics

The Micrometer library comes with a number of useful metrics provider, which can be easily added:

import io.micrometer.core.instrument.binder.jvm.*;
import io.micrometer.core.instrument.binder.system.*;


PrometheusMeterRegistry registry = new PrometheusMeterRegistry(PrometheusConfig.DEFAULT);

// add a tag to all reported values to simplify filtering in large installations:
registry.config().commonTags("application", "My-Application");

new ClassLoaderMetrics().bindTo(registry);
new JvmMemoryMetrics().bindTo(registry);
new JvmGcMetrics().bindTo(registry);
new JvmThreadMetrics().bindTo(registry);
new UptimeMetrics().bindTo(registry);
new ProcessorMetrics().bindTo(registry);
new DiskSpaceMetrics(new File(System.getProperty("user.dir"))).bindTo(registry);

MicrometerPlugin micrometerPlugin = MicrometerPlugin.Companion.create(micrometerConfig -> micrometerConfig.registry = registry);

Javalin app = Javalin.create(config -> {
    config.plugins.register(micrometerPlugin);
}).start(8080);

app.get("/prometheus", ctx -> ctx.contentType(TextFormat.CONTENT_TYPE_004).result(registry.scrape()));

Custom Meters

It’s also easy to provide custom meters, reporting application-specific values, for example the length of a job-queue, the number of logged in users, or other values. In the following example, just a random number is returned:

import io.micrometer.core.instrument.Gauge;

Gauge
  .builder("myapp_random", () -> (int) (Math.random() * 1000))
  .description("Random number from My-Application.")
  .strongReference(true)
  .register(registry);

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