[aspectj-users] Design Question Dynamic Interceptors

[Jason Weinstein <Jason.Weinstein@xxxxxxx>]

I am using LTW with use of aop.xml and a single "aj" file. However i 
don't really see how AspectJ supports the addition and deletion of 
Aspects at runtime. In a way i want to weave and unweave new 
pointcuts/advice at runtime. In fact i'd like for a user to be able to 
specify them.

I would like to be able to

1) Add and Remove interceptors at runtime. Interceptors apply at 
specific points in the code (pointcut). All of the points are not known 
at deploy time.

For instance i would like to be able to add and remove an around() 
advice for Class/Interface A Method X at runtime

2) I would like to be able to chain the Interceptors.

For instance for method X i would like to first apply Interceptor A, 
then Interceptor B, then call the original Method X (or skip it).

To accomplish this i came up with a little framework which manages an 
Interceptor Table/Chains
It allows for the dynamic addition and deletion of Interceptors as well 
as their chaining.
The framework code is called from the aspect "aj" file.
So largely these pointcuts are static. However the Interceptor behavior 
is dynamic. (I'm being very specific and don't have a *.*(..) pointcut)
The advice in the "aj" code simple calls into my framework which is kind 
of like a DI (dynamic invocation) framework.

The question is is there a way to dynamically add and remove new 
pointcuts/advice at runtime, and ensure the order they are woven?.

Some example code which illustrates some ideas is shown below.

   public pointcut DeliveryChannel_accept1(
       DeliveryChannel object) :
       execution(public MessageExchange 
javax.jbi.messaging.DeliveryChannel+.accept())
       && this(object);


   Object around(DeliveryChannel object,
                 long timeout)
                 throws MessagingException :
       DeliveryChannel_accept1(object, timeout) {
       Proceed proceed = new Proceed() 
{                                                        // This is the 
actual target code. At the end of an InterceptorChain this code may be 
called.
           public Object invoke(Object target, Object[] args) throws 
Exception {
               DeliveryChannel channel = (DeliveryChannel) target;
               long timeout = (Long) args[0];
               return proceed(channel, timeout);
           }
       };
       Object result = null;
       try {
           result = 
system.invoke(JBIConstants.KEY_DELIVERYCHANNEL_ACCEPT1, // This code 
calls my framework, which
                   thisJoinPoint, proceed);                            
                                                    //1. Looks up the 
list of Interceptors to apply (can be empty)
       } catch (MessagingException e) 
{                                                                              
//2. Runs each interceptor with args from JoinPoint passed in
           throw 
e;                                                                                                                 
//3. Calls the Proceed object which runs the actual target method
       } catch (RuntimeException e) {
           throw e;
       } catch (Exception e) {
           throw new RuntimeException(e);
       }
       return result;
   }


Interceptors have a simple api like

   public Object invoke(IInterceptorChain chain) throws Exception;

The InterceptorChain has methods like

   public String getKey();

   public void setKey(String key);

   public Object getTarget();

   public void setTarget(Object target);

   public Member getMember(); // Constructor or Method

   public void setMember(Member member);

   public Object[] getArgs();

   public void setArgs(Object[] args);

   public Object proceed() throws Exception;

Where proceed() is implemented something like

   public Object proceed() throws Exception {
       Object ret;
       if (getIter().hasNext()) { // Iter contains list of Interceptors
           ret = getIter().next().invoke(this);
       } else {
           wasTargetCalled = true;
           ret = getProceed().invoke(target, args);
       }
       return ret;
   }

and Proceed abject has simple api like

   public Object invoke(Object target, Object[] args) throws Exception;


The table of Interceptors has methods like

addKey(key, Interceptor)
getListForKey(key)
removeInterceptor(Interceptor)


There are a variety of types of Interceptors including basic ones which 
only run if Filter passes, etc