Re: JMX problems

[Amy Roh]

Costin,

Costin Manolache wrote:

Craig, Amy - or anyone who knows JMX, I need help :-)

I just can't find any way to add an attribute change listener
in the whole JMX spec, unless I have the instance of the model
mbean. And there is no way to get that instance.

I talked to Hans Hrasna in JMX team and I got the following answers.

It IS possible to manage all attribute changes via JMX and persist them using attribute change listener using the current spec.

It's up to the MBean owning the attribute of interest to create and send
attribute change notifications when the attribute change occurs. So the
NotificationBroadcaster interface has to be implemented by any MBean for which an attribute change is of interest.

Example: If an MBean called myMbean needs to notify registered listeners when its attribute:

String myString

is modified, myMbean creates and emits the following notification:

new AttributeChangeNotification(myMbean, sequenceNumber, timeStamp,
msg, "myString", "String", oldValue, newValue);


One just adds a NotificationListener. AttributeChangeNotification is emitted just like any other notification.

All query and get methods in MBeanServer return ObjectInstance -
i.e. name and class, but no 'instance'.
There is an 'addNotificationListener' that takes the object name -
but the spec ( and implementation ) doesn't allow this to register
attribute change listeners, and att changes are not sent to listeners registered with this method ( there is an "all other but
attribute changes" in the PDF file ).

NotificationListeners registered on an MBean will receive the
AttributeChangeNotifications just like any other notification. There is no such special type "attribute change listeners".

Hope this helps.
Amy

I'm stuck. I can add some code to the modeler mbean to work around, but the solution won't work for other mbeans.

What I want to do is find all attribute changes done via JMX and persist them - if you remember my old proposal. At the moment I'm not very sure
it can be implemented. The only possible solution to revive it would be
to force all attribute changes to go through a modeler-specific interface
or to require the use of the modeler for all mbeans.

Costin



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