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From "Amy Roh" <amy...@apache.org>
Subject Re: JMX problems
Date Tue, 19 Nov 2002 20:04:57 GMT
> Thanks Amy !
>
> That was my initial understanding.
>
> The problem is that the ModelMBean implementation in JMX-RI and MX4J
> don't seem to behave this way, and the spec wording is ( page 84 in the
> 1.1 PDF ):

I believe ModelMBean implementation in JMX-RI and MX4J behave this way for
all external Notification listeners.

>
>  "In the model MBean, AttributeChangeNotifications are sent to a separate
> set of listeners than those that other notifications would go to. All
other
> notifications should go to listeners who registered using the methods
> defined in the NotificationBroadcaster interface.
> AttributeChangeNotifications can also be sent to all notification
listeners
> simply by using the NotificationBroadcaster interface alone."
>
> Since we are using model mbeans, ACN are sent to the "separate set",
> and "all other" notifications go to listeners registered using
> NotificationBrodacaster. That's the current behavior for JMX-RI, MX4J and
> modeler.


I believe this is only true for AttributeChangeNotifications generated by
the internal mechanism that is enabled when a listener internal to the
ModelMBean is added with addAttributeChangeNotificationListener().

I think this was intended to allow implementing persistance on a per
ModelMBean basis and was not intended to deliver generic
AttributeChangeNotifications.


>
> Is there any clarification of the spec - or another part that I
overlooked?
>
> I understand that this particular restriction is only on model mbeans -
> and it would be possible for regular mbeans to send attribute changes
> to all listeners. So a possible solution would be to modify modeler
> and make it a "dynamic mbean" ( or keep it model mbean but not implement
> this separation ).
>
> Costin
>
>
>
> Amy Roh wrote:
>
> > 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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> >>
>
>
>
>
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