MBeans for changing resources - JMX in Action - page 116

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The DynamicMBeanSupport class provides an implementation for all the methods
from the DynamicMBean interface. Subclasses can override them, but these imple-
mentations should be good enough for most situations. The getAttribute() and
setAttribute() methods use introspection (using the java.lang.reflect pack-
age) to get and set the value of class member variables. In addition, the setAt-
tribute() method invokes the getType() method to discover the type of a
member variable whether the requester has proper access to an attribute as
defined by the MBean's management interface. If it is an invalid request, get-
Type() returns null . The invoke() method does something similar in that it also
uses introspection to invoke operations of the class.
The four methods that make using this class advantageous are addMBeanAt-
tribute() , addMBeanConstructor() , addMBeanOperation() , and buildDynamic-
MBeanInfo() . The add methods allow subclasses to create their MBeanInfo object
by adding portions of it as needed. For instance, look in the constructor of the
class: it invokes the addMBeanAttribute() method in order to expose the
description field of this MBean. Of course, it is not necessary to expose this
field, but doing so serves as a good example. The constructor also adds itself to
the MBeanInfo object. Finally, the buildDynamicMBeanInfo() method is called to
put everything together in an MBeanInfo instance as needed.

5.7 Summary

This chapter introduced you to a more complex type of MBean: the Dynamic
MBean. You learned that Dynamic MBeans are useful when managing evolving
resources or resources with unstable interfaces. In addition, you learned that
Dynamic MBeans generate their management interface at runtime using a stan-
dard set of JMX metadata classes. In addition to writing Dynamic MBeans, you
created a super class that can save you time and effort in future Dynamic MBean
development.
Chapter 6 covers the JMX notification model surrounding MBeans. That
chapter will teach you about using standard JMX notifications, creating your own
notifications, and receiving notifications from MBeans.