Communicating with JMX agents - JMX in Action - page 194

To receive notifications from a particular MBean, you simply invoke the add-
NotificationListener() method of the client. Because all Notification objects
are serializable, they can be transmitted over RMI to interested clients.

Connector heartbeat
The RMI connector uses a notification system to detect the health of the client
and/or server portions of the connector. When using an RmiConnectorClient
object, you can add a notification listener for receiving HeartBeatNotification
objects. A HeartBeatNotification object can indicate several conditions about a
connection to the RMI connector server, as listed in table 9.2. The values in the
Notification Type column are public static members of the HeartBeatNotifi-
cation class.

Table 9.2 Notification types used by a HeartBeatNotification notification

Notification type Description

A connection has been made between the client and server.

CONNECTION_ESTABLISHED

A connection has died.

CONNECTION_LOST

CONNECTION_REESTABLISHED A connection was temporarily unavailable, but is now connected.

The client is trying to reestablish a dead connection.

CONNECTION_RETRYING

The connection has been closed.

CONNECTION_TERMINATED

You acquire the condition value by invoking the getType() method of the notifi-
cation.

Client context checking
The last feature of the RMI connector covered in this chapter is the concept of a
client context checker. A context checker ensures that a client passes a pre-
defined test before it can invoke any methods on the remote MBean server.
The client must set an OperationalContext object into its RmiConnectorClient
object. The connector client object will pass this context to the RMI connector
server, which uses it to decide whether to complete a client's request on an MBean
server. To do so, the server uses an instance of the class MBeanServerChecker .
An MBeanServerChecker object encapsulates an MBeanServer object and con-
tains a check method for every method declared by the MBeanServer class. For
instance, for a client that attempted to invoke create Bean() on a remote MBean
server, the MBeanServerChecker would first invoke the method checkCreate() .
This method would verify the client's OperationalContext in some way and, if it