Re: [aspectj-users] Aspectj discussion

["Enrique J. Amodeo Rubio" <eamodeorubio@xxxxxxxxxxxxxx>]

Sean R. Drucker wrote:
> I would like to learn about "Weaving different advices for the same class at
> different times without stopping the JVM" as well.  If you find some source,
> please post it back this list.
>
> Thanks... Sean
>
> ----- Original Message ----- 
> From: "Mohan Radhakrishnan" <mradhakrishnan@xxxxxxxxxxxxxxxx>
> To: <aspectj-users@xxxxxxxxxxx>
> Sent: Tuesday, May 06, 2003 7:48 AM
> Subject: [aspectj-users] Aspectj discussion
>
>
> > Hi,
> >
> > I am a newbie. Is this a very low volume list? I am interested in using
> > aspects. Have read some of the code of the nanning project since it is a
> > framework using dynamic proxies etc.
> >
> >       Is there a more popular forum somewhere? I don't receive many mails.
> >
> > The idea is to learn about
> > 1. Reusable aspects.
> > 2. Weaving diffent advices for the same class at different times withou t
> > stopping the JVM.
> > 3. Aspect patterns
> >
> > Mohan
> >
> > _______________________________________________
> > aspectj-users mailing list
> > aspectj-users@xxxxxxxxxxx
> > http://dev.eclipse.org/mailman/listinfo/aspectj-users
> >
> >   
>
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"Weaving diffent advices for the same class at different times without stopping the JVM." If you mean with this changing the behavior of an advice at runtime, you could use an approach based on delegating advice code to commands. You could have a class that decides which command to execute. Here is a draft to give you some ideas (not compiled, untested code follows):

- Have a generic command interface:
public interface ICommand
{
// p contains info about the JoinPoint that executed this command
// Additional parameters would be necessary.
  public Object doAdvice(JoinPoint p);
}

-Have a command manager that decides what command to execute. This
decision could be taken using configuration files(for static desicions)
and/or the state of your system (for runtime decision).
public interface ICommandManager
{
    public boolean hasCommand(String key);
    public void setCommand(String key, ICommand c);
    public void removeCommand(String key);

    public ICommand getCommand(String key) throws
CommandNotFoundException;
}
Note that you can modify at runtime the commands avalaible for a given
key. Each key could represent an unique name for advices. For example,
using an administration application, an administrator could associate
commands with advices at runtime or change that associations. This
results in changes in runtime behaviour of the system.

- Finally you could use all of this from an advice in an aspect:
package sample;
public aspect MyAspect
{
    ...
    pointcut mypointcut(): call(* sample.otherpackage.*.set*(..));

    before(): mypointcut()
    {
        try
        {
            ICommand
delegate=getCommandManager().getCommand("sample.MyAspect.mypointcut.before");
            delegate.doAdvice(thisJoinPoint);
            }catch(CommandNotFoundException ex)
           {
                // If not command found do nothing.              
            }
    }
    ...
}

Of course this approach doesn't allow to change a pointcut's definition
at runtime. If you want this you should look for another AOP language or
framework. 

Hope this helps you,
    Enrique J. Amodeo Rubio