Sun GlassFish Enterprise Server 2.1 Developer's Guide

MBean Notifications

All AMX MBeans that emit Notifications place a java.util.Map within the UserData field of a standard JMX Notification, which can be obtained using Notification.getUserData(). Within the map are one or more items, which vary according to the Notification type. Each Notification type, and the data available within the Notification, is defined in the Javadoc of the MBean (AMX interface) that emits it.

Note that certain standard Notifications, such as (see do not and cannot follow this behavior.