A key component of the agent level is the managed bean server. Its functionality is exposed through an instance of the javax.management.MBeanServer. An MBean server is a registry for MBeans that makes the MBean management interface available for use by management applications. The MBean never directly exposes the MBean object itself; rather, its management interface is exposed through metadata and operations available in the MBean server interface. This provides a loose coupling between management applications and the MBeans they manage.

MBeans can be instantiated and registered with the MBeanServer by the following:

• Another MBean

• The agent itself

• A remote management application (through the distributed services)

When you register an MBean, you must assign it a unique object name. The object name then becomes the unique handle by which management applications identify the object on which to perform management operations. The operations available on MBeans through the MBean server include the following:

• Discovering the management interface of MBeans

• Reading and writing attribute values

• Invoking operations defined by MBeans

• Registering for notifications events

• Querying MBeans based on their object name or their attribute values

Protocol adaptors and connectors are required to access the MBeanServer from outside the agent's JVM. Each adaptor provides a view via its protocol of all MBeans registered in the MBean server the adaptor connects to. An example adaptor is an HTML adaptor that allows for the inspection and editing of MBeans using a Web browser. As was indicated in Figure 3.2, “The Relationship between the components of the JMX architecture”, there are no protocol adaptors defined by the current JMX specification. Later versions of the specification will address the need for remote access protocols in standard ways.

A connector is an interface used by management applications to provide a common API for accessing the MBean server in a manner that is independent of the underlying communication protocol. Each connector type provides the same remote interface over a different protocol. This allows a remote management application to connect to an agent transparently through the network, regardless of the protocol. The specification of the remote management interface will be addressed in a future version of the JMX specification.

Adaptors and connectors make all MBean server operations available to a remote management application. For an agent to be manageable from outside of its JVM, it must include at least one protocol adaptor or connector. JBoss currently includes a custom HTML adaptor implementation and a custom JBoss RMI adaptor.