How can I use the Prometheus Java client library?

Can you show me some examples of using the Prometheus Java client library?

Sure! The Prometheus Java client library allows you to instrument your Java applications. For example, you can create a simple counter like this:

import io.prometheus.client.Counter;

public class Example {
    static final Counter requests = Counter.build()
        .name("requests_total")
        .help("Total number of requests.")
        .register();

    public void handleRequest() {
        requests.inc(); // Increment the counter
        // Handle the request
    }
}

What about creating a gauge?

To create a gauge, you can use the following code:

import io.prometheus.client.Gauge;

public class Example {
    static final Gauge temperature = Gauge.build()
        .name("temperature_celsius")
        .help("Current temperature in Celsius.")
        .register();

    public void updateTemperature(double temp) {
        temperature.set(temp); // Set the gauge value
    }
}

How do I expose these metrics to Prometheus?

You can expose metrics by setting up an HTTP server. Here's a simple example:

import io.prometheus.client.exporter.HTTPServer;

public class Example {
    public static void main(String[] args) throws Exception {
        HTTPServer server = new HTTPServer(1234); // Start server on port 1234
    }
}