JMX Metrics Quick Access with Java

HiveMQ, a robust and highly configurable MQTT broker, extends its functionality by offering an extensive array of metrics via Java Management Extensions (JMX): https://docs.hivemq.com/hivemq/latest/user-guide/monitoring.html#jmx. This empowers users to engage in efficient monitoring through widely recognized JMX monitoring tools like JConsole.

In addition to the plethora of visualization tools like Prometheus, Grafana, and Datadog available in the realm of monitoring, there is substantial merit in acquiring an overview of these metrics using pure Java tooling. This article serves as a comprehensive resource, offering practical Java examples for listing all accessible metrics and facilitating the extraction of metric values.

Instructions

List all available metrics

import javax.management.*;
import javax.management.remote.JMXConnector;
import javax.management.remote.JMXConnectorFactory;
import javax.management.remote.JMXServiceURL;
import java.util.Set;

/**
 * This class demonstrates how to list JMX namespaces and MBeans on a remote JMX server.
 */
public class JMXListAllMetrics {
    /**
     * The main entry point of the program.
     *
     * @param args Command-line arguments (not used in this example).
     */
    public static void main(String[] args) {
        // Press Opt+Enter with your caret at the highlighted text to see how
        // IntelliJ IDEA suggests fixing it.
        System.out.printf("Hello and welcome!");

        // Define the JMX server URL
        String jmxUrl = "service:jmx:rmi:///jndi/rmi://localhost:9010/jmxrmi";

        try {
            // Create a JMX connector to connect to the remote JMX server
            JMXServiceURL serviceURL = new JMXServiceURL(jmxUrl);
            JMXConnector connector = JMXConnectorFactory.connect(serviceURL);

            // Connect to the MBean server
            MBeanServerConnection mbeanServerConnection = connector.getMBeanServerConnection();

            // List all MBeans and their object names
            System.out.println("Listing all MBeans and their namespaces:");
            Set<ObjectName> mbeanNames = mbeanServerConnection.queryNames(null, null);
            for (ObjectName mbeanName : mbeanNames) {
                //System.out.println("MBean: " + mbeanName);
                String namespace = mbeanName.getDomain(); // Extract the namespace
                //System.out.println("Namespace: " + namespace);
                System.out.println(namespace + " " + mbeanName);
            }

            // Close the JMX connector
            connector.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Compilation
javac JMXListAllMetrics.java
Execution
java JMXListAllMetrics

Scrape one metric periodically

import javax.management.*;
import javax.management.remote.JMXConnector;
import javax.management.remote.JMXConnectorFactory;
import javax.management.remote.JMXServiceURL;

/**
 * This class represents a JMX client that connects to a remote JMX server to retrieve and print
 * attribute values of a specified MBean (Managed Bean) object at regular intervals.
 */
public class JMXOneMetric {

    /**
     * The main entry point of the JMX client application.
     *
     * @param args Command-line arguments. Expects two arguments: <ObjectName> and <DelayInMillis>.
     *             <ObjectName> specifies the target MBean's ObjectName, and <DelayInMillis> is
     *             the delay between metric checks in milliseconds.
     *             Example: java JMXClient metrics:name=com.hivemq.jvm.memory.heap.used 2000
     * @throws Exception If there are errors in the JMX connection or attribute retrieval.
     */
    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            System.err.println("Usage: java JMXClient <ObjectName> <DelayInMillis>");
            System.err.println("Example: java JMXClient metrics:name=com.hivemq.jvm.memory.heap.used 2000");
            System.exit(1);
        }

        // Parse command-line arguments
        String objectNameStr = args[0];
        long delayInMillis = Long.parseLong(args[1]);

        // Define the JMX service URL for connecting to the remote JMX server
        String jmxUrl = "service:jmx:rmi:///jndi/rmi://localhost:9010/jmxrmi";
        JMXServiceURL serviceURL = new JMXServiceURL(jmxUrl);
        JMXConnector connector = JMXConnectorFactory.connect(serviceURL);
        MBeanServerConnection connection = connector.getMBeanServerConnection();

        // Define the ObjectName based on the command-line argument
        ObjectName mbeanName = new ObjectName(objectNameStr);

        // Run indefinitely with the specified delay between checks
        while (true) {
            // Fetch and print the metric value
            Object metricValue = connection.getAttribute(mbeanName, "Value");
            System.out.println(objectNameStr + " " + metricValue);

            // Sleep for the specified delay before the next check
            Thread.sleep(delayInMillis);
        }
    }
}

Compilation
javac JMXOneMetric.java
Execution
java JMXOneMetric <ObjectName> <DelayInMillis>
Replace <ObjectName> with the desired metric's ObjectName and <DelayInMillis> with the desired delay between checks in milliseconds.

Dependencies for JMX are already included in the JDK, making it easy to access and monitor HiveMQ metrics with these Java programs.

Note: Ensure that you have the necessary permissions and network access to connect to the remote JMX server and access the HiveMQ metrics:

https://docs.hivemq.com/hivemq/latest/user-guide/monitoring.html#_configuration

JMX Metrics Quick Access with Java

Instructions

List all available metrics

Scrape one metric periodically

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