The first page displayed by the HTML adaptor is always the agent view. It initially contains a list of all registered MBeans. The following figure shows the agent view for the minimal agent. It contains four MBeans: three communication MBeans, one of which is the HTML adaptor, and the MBean server delegate. The delegate is a special MBean explained in MBean Server Delegate.
The text field for filtering by object name enables you to modify the list of displayed MBeans. The filter string is initially *:*, which displays all registered MBeans. Filtering MBeans describes how to use the filter. The agent's registered domain indicates the name of the default domain in this agent. The number of MBeans on this page is the count of those listed beneath the separator line.
The Admin button is links to the agent administration page (see Agent Administration).
The MBean list contains all MBeans whose object name matches the filter string. Object names can be filtered by their domain name and list of key-value pairs. In this list, MBeans are sorted and grouped by domain name. Each MBean name listed is an active link to the page of the corresponding MBean view.
After its initialization, the contents of an agent are dynamic. New MBeans can be created and registered into new or existing domains and old MBeans can be removed. These changes can also affect the functionality of the agent. New agent services can be registered (or removed) as well. We will demonstrate examples of dynamic management in Instantiating and Managing MBeans.
The MBean server delegate is an MBean that is automatically instantiated and registered by the MBean server when it is created. It provides information about the version of the Java Dynamic Management Kit (DMK) that is running, and it represents the MBean server when sending notifications.
Notifications are events sent by MBeans. They are covered in detail in Chapter 9, Notification Mechanism. Because the MBean server instance is not an MBean object, it relies on its delegate MBean to send notifications. The MBean server delegate sends notifications to inform interested listeners about such events as MBean registrations and unregistrations.
The exposed attributes of the delegate MBean provide vendor and version information about the MBean server. This can let a remote management application know which agent version is running and which version of the Java runtime environment it is using. The delegate MBean also provides a unique identification string for its MBean server.