Home » Enterprise Java » jmx » Send notification at MBean attribute change

About Ilias Tsagklis

Avatar photo
Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.

Send notification at MBean attribute change

This is an example of how to send a notification when an attribute of an MBean changes. An MBean is a managed Java object, similar to a JavaBeans component, that follows the design patterns set forth in the JMX specification. An MBean can represent a device, an application, or any resource that needs to be managed. MBeans expose a management interface that consists of a set of readable or writable attributes, or both, a set of invokable operations and a self-description. The JMX API also defines a mechanism to enable MBeans to generate notifications, for example, to signal a state change, a detected event, or a problem. Here, we will create an MBean and register it to MBeanServer, and then generate a notification when an attribute of the MBean changes. In short, the steps we will follow are:

  • Create a Java interface, HelloBean. Every method in the interface defines either an attribute or an operation in the MBean. The interface has a method, sayHello() a read-write attribute called message of type String. This is the attribute on whose change we will send the notification.
  • Create a Java class, Hello that implements that interface and also extends NotificationBroadcasterSupport so as to be able to generate notifications. In its constructor it uses addNotificationListener(NotificationListener listener, NotificationFilter filter, Object handback) API method of NotificationBroadcasterSupport, so as to add a listener. In this method it overrides the handleNotification(NotificationListener listener, Notification notif, Object handback) method of NotificationBroadcasterSupport, where it prints the notification it handles. The notification has a source that is the name of the MBean, and we can get it using getMessage() Notification API method and it also has a sequence number that we can get using getSequenceNumber() Notification API method. In the setMessage(String message) method, the old message is held in a variable and then a new AttributeChangeNotification is created for the new message, increasing the sequence number of notifications and then the sendNotification(Notification notification) API method of NotificationBroadcasterSupport is used to send the notification.
  • Create an MBeanServer that is the interface for MBean manipulation on the agent side. Use getPlatformMBeanServer() API method of ManagementFactory.
  • Define the object name for the MBean. The object name is an instance of the JMX class ObjectName and must contain a domain and a list of key-properties.
  • Create a new instance of the MBean and register it to MBeanServer, using registerMBean(Object object, ObjectName name) API method of MBeanServer.
  • Use getAttribute(ObjectName name, String attribute) API method of MBeanServer to get the value of a specific attribute of the MBean.
  • Use setAttribute(ObjectName name, Attribute attribute) API method of MBeanServer to change the value of the same attribute of the MBean and then get the attribute’s value again.

Let’s take a look at the code snippet that follows:  

package com.javacodegeeks.snippets.enterprise;

import java.lang.management.ManagementFactory;

import javax.management.Attribute;
import javax.management.AttributeChangeNotification;
import javax.management.MBeanServer;
import javax.management.Notification;
import javax.management.NotificationBroadcasterSupport;
import javax.management.NotificationListener;
import javax.management.ObjectName;

public class SendNotificationAtMBeanAttributeChange {
	
	public static void main(String[] args) throws Exception {
		
		String objectName = "com.javacodegeeks.snippets.enterprise:type=Hello";
		
		MBeanServer server = ManagementFactory.getPlatformMBeanServer();

	    // Construct the ObjectName for the Hello MBean we will register
	    ObjectName mbeanName = new ObjectName(objectName);
	    
	    Hello mbean = new Hello();
	    
	    server.registerMBean(mbean, mbeanName);
	    
	    // print the default message
	    String currentMessage = (String) server.getAttribute(mbeanName, "Message");
	    System.out.println("Current Message: " + currentMessage);
	    
	    // change the attribute value
	    String newMessage = "Hello Java Code Geeks";
	    server.setAttribute(mbeanName, new Attribute("Message", newMessage));
	    
	    // print the new message
	    currentMessage = (String) server.getAttribute(mbeanName, "Message");
	    System.out.println("Current Message: " + currentMessage);
		
	}
	
	public static class Hello extends NotificationBroadcasterSupport implements HelloMBean {
		
		private long sequenceNumber = 1;
		private String message = "Hello World";
		
		public Hello() {
			addNotificationListener(new NotificationListener() {
				@Override
				public void handleNotification(Notification notification, Object handback) {
					System.out.println("*** Handling new notification ***");
					System.out.println("Message: " + notification.getMessage());
					System.out.println("Seq: " + notification.getSequenceNumber());
					System.out.println("*********************************");
				}
			}, null, null);
		}

		@Override
		public String getMessage() {
			return this.message;
		}

		@Override
		public void sayHello() {
			System.out.println(message);
		}

		@Override
		public void setMessage(String message) {
			String oldMessage = this.message;
			this.message = message;
			Notification n = new AttributeChangeNotification(this, sequenceNumber++,
			
  System.currentTimeMillis(), "Message changed", "Message", "String",
			
  oldMessage, this.message);
			sendNotification(n);
		}
		
	}
	
	public static interface HelloMBean {
		
		// operations
		
		public void sayHello();

		// attributes
		
		// a read-write attribute called Message of type String
		public String getMessage();
		public void setMessage(String message);
		
	}

}

  
This was an example of how to send a notification when an attribute of an MBean changes in Java.

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

 

and many more ....

 

Receive Java & Developer job alerts in your Area

I have read and agree to the terms & conditions

 

Subscribe
Notify of
guest

This site uses Akismet to reduce spam. Learn how your comment data is processed.

0 Comments
Inline Feedbacks
View all comments