30.1 JMX Modern

Expose runtime metrics and management operations via JMX for monitoring and operational control.

Creating an MBean

public interface AppStatsMXBean {
  int getActiveRequests();
  long getTotalRequestsProcessed();
  void reset();
}

public class AppStats implements AppStatsMXBean {
  private final AtomicInteger active = new AtomicInteger();
  private final AtomicLong total = new AtomicLong();

  public int getActiveRequests() { return active.get(); }
  public long getTotalRequestsProcessed() { return total.get(); }
  public void reset() { active.set(0); total.set(0); }

  public void recordRequest() { active.incrementAndGet(); total.incrementAndGet(); }
  public void completeRequest() { active.decrementAndGet(); }
}

Registering MBean

import java.lang.management.ManagementFactory;
import javax.management.*;

AppStats stats = new AppStats();
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
ObjectName name = new ObjectName("com.example:type=AppStats");
mbs.registerMBean(stats, name);

Remote JMX Access

java -Dcom.sun.management.jmxremote \
     -Dcom.sun.management.jmxremote.port=9010 \
     -Dcom.sun.management.jmxremote.authenticate=false \
     -Dcom.sun.management.jmxremote.ssl=false \
     MyApp

Connect with jconsole localhost:9010 or VisualVM.

Querying MBeans Programmatically

MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
ObjectName name = new ObjectName("com.example:type=AppStats");
int active = (Integer) mbs.getAttribute(name, "ActiveRequests");

Integration with Micrometer

For modern observability, consider Micrometer (exposes metrics to Prometheus, Grafana):

import io.micrometer.core.instrument.*;

MeterRegistry registry = new SimpleMeterRegistry();
Counter requests = registry.counter("app.requests.total");
Gauge.builder("app.requests.active", stats, AppStats::getActiveRequests)
    .register(registry);

Guidance

• Use MBeans for operational metrics and admin operations.
• Secure remote JMX with authentication and SSL in production.
• Prefer modern metric libraries (Micrometer, OpenTelemetry) for cloud-native apps.
• Avoid exposing sensitive operations (restart, config changes) without authorization.