JMX: Notification Support

JMX provide APIs to enable MBeans to generate notifications. By using this, you can receive notifications whenever some operation is performed by MBean.

How to generate notifications?

MBean class must implement interface NotificationEmitter or extend NotificationBroadcasterSupport. By calling the sendNotification method, you can broad cast the notification to correspondent listeners.

How to receive notifications?

By adding notification listeners to MBean object, you can receive notifications.

Example

SystemStatistics mbean = new SystemStatistics();
mbean.addNotificationListener(new StatsListener(), null, null);

Find the below working application.

SystemStatisticsMBean.java

package com.sample.mbeans;

public interface SystemStatisticsMBean {

	public int readCount();

	public int incrementReadCount();

	public int decrementReadCount();

	public int writeCount();

	public int incrementWriteCount();

	public int decrementWriteCount();

}

SystemStatistics.java

package com.sample.mbeans;

import javax.management.Notification;
import javax.management.NotificationBroadcasterSupport;

public class SystemStatistics extends NotificationBroadcasterSupport implements SystemStatisticsMBean {

	private int readCount = 0;
	private int writeCount = 0;
	private static int sequenctNumber = 1;

	public int getReadCount() {
		return readCount;
	}

	public void setReadCount(int readCount) {
		this.readCount = readCount;
	}

	public int getWriteCount() {
		return writeCount;
	}

	public void setWriteCount(int writeCount) {
		this.writeCount = writeCount;
	}

	@Override
	public int readCount() {
		return readCount;
	}

	@Override
	public int incrementReadCount() {
		readCount++;
		Notification notification = new Notification("com.sample.mbeans.SystemStatistics", this, sequenctNumber++,
				System.currentTimeMillis(), "Read Count is incremented to " + readCount);
		sendNotification(notification);
		return readCount;
	}

	@Override
	public int decrementReadCount() {
		return --readCount;
	}

	@Override
	public int writeCount() {
		return writeCount;
	}

	@Override
	public int incrementWriteCount() {
		return ++writeCount;
	}

	@Override
	public int decrementWriteCount() {
		return --writeCount;
	}

}

StatsListener.java

package com.sample.listeners;

import javax.management.Notification;
import javax.management.NotificationListener;

public class StatsListener implements NotificationListener{

	@Override
	public void handleNotification(Notification notification, Object handback) {
		System.out.println("Receiving notification...");
		System.out.println(notification.getType());
		System.out.println(notification.getMessage());
	}

}

StatsAgent.java

package com.sample.agents;

import java.lang.management.ManagementFactory;

import javax.management.InstanceAlreadyExistsException;
import javax.management.MBeanRegistrationException;
import javax.management.MBeanServer;
import javax.management.MalformedObjectNameException;
import javax.management.NotCompliantMBeanException;
import javax.management.ObjectName;

import com.sample.listeners.StatsListener;
import com.sample.mbeans.SystemStatistics;

public class StatsAgent {
	private MBeanServer mbs;
	private SystemStatistics mbean;

	public StatsAgent() throws MalformedObjectNameException, InstanceAlreadyExistsException, MBeanRegistrationException,
			NotCompliantMBeanException {
		ObjectName name = new ObjectName("com.sample.mbean.interfaces:type=SystemStatisticsMBean");
		mbean = new SystemStatistics();

		mbs = ManagementFactory.getPlatformMBeanServer();
		mbs.registerMBean(mbean, name);

		mbean.addNotificationListener(new StatsListener(), null, null);
	}

}

Application.java

package com.sample.app;

import com.sample.agents.StatsAgent;

public class Application {

	public static void main(String[] args) throws Exception {
		new StatsAgent();

		System.out.println("Waiting forever...");
		Thread.sleep(Long.MAX_VALUE);

	}

}

Run the application.

Open command prompt (or) terminal, execute jconsole command.

Select ‘com.sample.app.Application’ process, click on Connect button.

If you see above kind of screen, click on ‘Insecure Connection’ button.

Go to MBeans tab.

Select ‘incrementReadCount’ under Operations.

Click on ‘incrementReadCount’ button.

You can see return value of ‘incrementReadCount’ function.

In the application console, you will get below notifications.

Waiting forever...

Receiving notification...

com.sample.mbeans.SystemStatistics

Read Count is incremented to 1

Click again on incrementReadCount button.

You can see below messages in the console.

Receiving notification...

com.sample.mbeans.SystemStatistics

Read Count is incremented to 2

I hope you understand the JMX notification mechanism

Previous                                                 Next                                                 Home