8.2.1 NotificationEmitter Interface

A class must implement the NotificationEmitter interface to be recognized as a source of notifications in the JMX architecture. This interface provides the methods for adding or removing a notification listener to or from the emitter. When the emitter sends a notification, it must send it to all listeners that are currently registered through this interface.

This interface also specifies a method that returns information about all notifications that might be sent by the emitter. This method returns an array of MBeanNotificationInfo objects, each of which provides a name, a description string, and the type string of the notification.

As detailed in the Javadoc API, the MBeanServerDelegate class implements the NotificationEmitter interface. We know from the JMX specification that it sends notifications of the following types:

• JMX.mbean.registered

• JMX.mbean.unregistered

Although emitter objects are almost always MBeans, they should not expose the methods of the NotificationEmitter interface. That is, the MBean interface of a standard MBean should never extend the NotificationEmitter interface. As we shall see in Chapter 22, Notification Forwarding in Legacy Connectors, the remote connector clients provide the methods needed to register for and receive notifications remotely.

The NotificationEmitter should be used in preference to the old NotificationBroadcaster class.