Re: [aspectj-users] Examining a destructive read in an aspect

[Grey, Lee]

I think I have a solution, but I'm not sure whether it violates a best practice 
(or is just beneath a good aspect developer):

I created a ThreadLocal<Boolean> to determine which invocations should be 
advised and which should not:

 private static final ThreadLocal<Boolean> tlAdvise = new 
ThreadLocal<Boolean>() {
  @Override protected Boolean initialValue() { return true; }
 };
Then I set the ThreadLocal to false when I want to run the real methods and to 
true when I want them to be short-circuited with my own advise:

    ...
  tlAdvise.set(false);
  if( ctx.hasNextIncoming() ) {    // call the real Sonic code
   System.out.println("In beforeCallToService: hasNextIncoming returned true");
   XQEnvelope env = ctx.getNextIncoming();    // call the real Sonic code
   tlAdvise.set(true);
    ...
My pointcuts use if:

    pointcut hasIncoming() :
     execution(boolean XQServiceContext.hasNextIncoming()) &&
     if(tlAdvise.get());
and

    pointcut getIncoming() :
     execution(XQEnvelope XQServiceContext.getNextIncoming()) &&
     if(tlAdvise.get());
Is this a brute-force solution to something that could be done far more 
elegantly and efficiently with just a little more pointcut knowledge?  Is there 
anything that makes this a bad idea?

Thanks for your insights,
Lee

________________________________
From: aspectj-users-boun...@eclipse.org 
[mailto:aspectj-users-boun...@eclipse.org] On Behalf Of Grey, Lee
Sent: Wednesday, February 02, 2011 11:45 PM
To: aspectj-users@eclipse.org
Subject: Re: [aspectj-users] Examining a destructive read in an aspect

I've done what you suggested, and I think it would work fine, except that I 
can't get the pointcut right for the two calls I need to intercept.  I seem to 
be getting all or nothing.

What pointcut would intercept the calls to ctx.hasNextIncoming() and 
ctx.getNextIncoming() when they come from the actual XQServiceEx.service() 
method but would still make the real, unadulterated calls when made from inside 
my aspect?

My failed attempts include

pointcut hasIncoming() : call(boolean XQServiceContext.hasNextIncoming()) && 
!within(com.sonicsw..*);

pointcut getIncoming(XQServiceContext ctx) : call(XQEnvelope 
XQServiceContext.getNextIncoming()) && target(ctx) && (within(XQService) || 
within(XQServiceEx));

and other unsuccessful flailing.  I find creating successful pointcuts to be 
black magic.

Thanks,
Lee

________________________________
From: aspectj-users-boun...@eclipse.org 
[mailto:aspectj-users-boun...@eclipse.org] On Behalf Of Ramnivas Laddad
Sent: Monday, January 31, 2011 8:50 PM
To: aspectj-users@eclipse.org
Subject: Re: [aspectj-users] Examining a destructive read in an aspect

You could do something along the following lines:
1. In your before advice read destructively as needed and store away the result 
'env' in a ThreadLocal.
2. Advise ctx.getNextIncoming() with an around advice to return the stored 
result (and don't call proceed() in it).

-Ramnivas

On Mon, Jan 31, 2011 at 2:59 PM, Grey, Lee 
<lee.g...@ncr.com<mailto:lee.g...@ncr.com>> wrote:
I've been working on intercepting the service() method invocation in a Sonic 
ESB container.  I had just started to write my before() advice when the bad 
news dawned on me.  Just about every ESB service() method starts with the 
following...

   public void service(XQServiceContext ctx) throws XQServiceException {
        XQEnvelope env = null;
        while (ctx.hasNextIncoming()) {
            env = ctx.getNextIncoming();
            if (env != null) {
                XQMessage msg = env.getMessage();
That call to ctx.getNextIncoming() is a destructive read that returns a 
different XQEnvelope every time it's called.  The problem is that I need to 
evaluate the contents of the message that comes from ctx.getNextIncoming() in 
my before() advice.  What that means is that the call to ctx.getNextIncoming() 
in the service() method is not going to get the message, because the before() 
advice already got it.

Now I'm wondering if there's a way to put an aspect around 
ctx.getNextIncoming() to make it deliver the message again.  Or if I can 
somehow clone ctx so that I can read the cloned message in before() and then 
read it from the real XQServiceContext object in service().  XQServiceContext 
doesn't offer any way to peek or browse, and it doesn't have a method to put a 
message, either.

I would imagine I'm not the first person to run into this kind of issue with 
AOP before.  I'm hoping that there's a pattern to address it.

Thanks,
Lee Grey

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