3 Replies Latest reply on Aug 17, 2005 8:25 AM by Ryan McDonough

    aop: one-way events ?

    etienne antoniutti di muro Newbie

      Hi everybody,
      I am thinking to the following:
      1- aop is great for 'eventizing' applications through interceptors. Intercepting application activites, turns applications into 'event producers' each time a pointcut is reached (method call, field access, ....), and you can use such events to do all the nice things you want to improve your app. But this is just one-way: application->interceptor.

      2- ...but, lets say I'd like to do this in reverse. I want my application to be an 'event consumer', that is, via my aop interceptors I want to inject 'events', i.e. method calls, set fields, into my application without the need to wait an application pointcut to be reached,
      making aop a two-way street: application <-> interceptor.

      Is this feasible ?
      Is this supported by the aop model ? - If so, How ?


        • 1. Re: aop: one-way events ?
          Ryan McDonough Newbie

          It sounds like you want to use an Introduction + a Mixin. Have a look at the docs for more information on the topic. Do you have a specific example in mind for what you want to do?


          • 2. Re: aop: one-way events ?
            etienne antoniutti di muro Newbie

            Hi Ryan, tnx for your post. Sorry for delay, but in Italy we had a short mid-summer holiday :)

            Had a look to Introductions+Mixins, it might be what I am looking for.
            The idea is to use AOP to build a set of "sensors" and "actuators" to observe and control application behaviour. Instead of re-write legacy application code or hard code this feature in new apps, AOP is the right solution, because:
            - it is a separate concern
            - avoids adding complexity to code.

            What I am doing right now, is designing a control-theoretic model of a middleware layer. I need to observe the classes I have, i.e. throughput between classes, latency, resource allocation ... , and modify some internal parameters in order to control behaviour at system level. It is a closed loop.
            Briefly, the structure i'd like to adopt is the following:

             -------> control logic ----------
             | |
             | V
            AOP { sensor actuator
             ^ |
             | V

            An AOP layer is built on top of the application and a contol layer is built on top of it.

            The "sensors" are the easiest part: at runtime the application generates events, that the AOP layer interceps, and the control layer processes.
            "Actuators" are tricky: the control layer generates 'control events' that the actuators should route back to the application.
            Still a question: even if I create a mixin class, and transparently add the features I need to access its inner data, I need a reference of my class into the AOP layer, otherwise how do I enable it to consume events?


            • 3. Re: aop: one-way events ?
              Ryan McDonough Newbie

              I wrote an aspect recently that gives a POJO bound property support. I used an introduction+mixin to add the property change support to the POJO. A second aspect is used to monitor the fields of the POJO for any changes. If a change occurs, the aspect then fires a property change event to all registered listeners. I have a typo-ladden page up here:


              You can read more about it there. Without knowing anything inparticular about the POJO I'm advising, I'm able to be notified whenever a field value changes. I think what I'm doing here might be similar to what you are trying to do. Let me know if this helps any.This stuff is way cool!