2.1.4 Open MBeans

Open MBeans allow management applications and the users to understand and use new managed objects as the objects are discovered at runtime. These MBeans are called open because they rely on a small, predefined set of universal Java types and they advertise their functionality.

Management applications and open MBeans are thus able to share and use management data and operations at runtime without requiring the recompiling, reassembly, or expensive dynamic linking of management applications. In the same way, human operators can use the newly discovered managed object intelligently without having to consult additional documentation.

To provide its own description to management applications, an open MBean must be a dynamic MBean. Beyond the DynamicMBean interface, no corresponding open interface exists that must be implemented. Instead, an MBean earns its openness by providing a descriptively rich metadata and by using only certain predefined data types in its management interface.

An open MBean has attributes, operations, constructors, and possibly notifications like any other MBeans. An open MBean is a dynamic MBean with the same behavior and all of the same functionality. An open MBean also has the responsibility of providing its own description. However, all of the object types that the MBean manipulates, its attribute types, its operation parameters and return types, and its constructor parameters, must belong to a defined set of basic data types. It is the developer's responsibility to implement the open MBean fully by using these data types only.

An MBean indicates whether it is open or not through the MBeanInfo object it returns. Open MBeans return an OpenMBeanInfo interface. This interface is implemented by OpenMBeanInfoSupport, which inherits from MBeanInfo. If an MBean is marked as open in this manner, it is a guarantee that a management application compliant with the JMX specification can immediately make use of all attributes and operations without requiring additional classes.

Since open MBeans are also dynamic MBeans and they provide their own description, the MBean server does not check the accuracy of the OpenMBeanInfo object. The developer of an open MBean must guarantee that the management interface relies on the basic data types and provides a rich, human-readable description. As a rule, the description provided by the various parts of an open MBean must be suitable for displaying to a user through a graphical user interface (GUI).