| Add argument to field set joinpoint ? Was: Re: [aspectj-users] Question re: declare error |
Pete,
When used with get/set the pointcut this & target match the object accessing the field and the one that defines it respectively.There is no pointcut to match the field itself although you could image one: "field()" for example. But there are problems. Like this & target it must be typed but you can't just use Object because of primitive fields. But it gets worse because in AspectJ any pointcut combination is possible - they are orthogonal - although certain combinations are not very useful because they match nothing e.g. call & execution. The "field()" pointcut would be _undefined_ at certain join points which is messy.
Matthew Webster
AOSD Project
Java Technology Centre, MP146
IBM Hursley Park, Winchester, SO21 2JN, England
Telephone: +44 196 2816139 (external) 246139 (internal)
Email: Matthew Webster/UK/IBM @ IBMGB, matthew_webster@xxxxxxxxxx
http://w3.hursley.ibm.com/~websterm/
14/09/2006 23:17
aspectj-users@xxxxxxxxxxx
aspectj-users@xxxxxxxxxxx Re: [aspectj-users] Question re: declare error
Yes, but that solution requires specific knowledge of the field you are pointcutting on. In general, I need to write one pointcut that services many objects with many different fields. Otherwise I might as well manually inline my undo / transaction rollback facility.
-pete
On 9/14/06, Vincent Jorrand <vjorrand@xxxxxxxxx > wrote:
Matthew Webster's post actually mentions 2 solutions, one of which uses a priviledged aspect and no reflection.
The following is copied from his post:
public class SomeClass {
private int intField;
public void setInt (int i) {
intField = i;
}
}
public privileged aspect PrivilegedAspect {
pointcut intFieldSet(SomeClass obj, int newValue) :
set(* intField) && target(obj) && args(newValue)
&& withincode(* SomeClass+.set*(..))
;
before (SomeClass obj, int newValue) : intFieldSet (obj,newValue) {
int oldValue = obj.intField;
System.out.println("?
beforeIntFieldSet() oldVaue=" + oldValue
+ ", newValue=" + newValue);
}
}
Vincent
----- Original Message ----
From: Peter Murray <pete@xxxxxxxxxxxx >
To: aspectj-users@xxxxxxxxxxx
Sent: Thursday, September 14, 2006 5:12:00 PM
Subject: Re: [aspectj-users] Question re: declare error
I wonder if there would be support in the AspectJ community for adding an additional "argument" to the set property that could optionally be bound using syntax like
... set(* *) && args(newValue, oldValue) ...
which would send in the old value?
Any thoughts? Am I off in the weeds - or is this technically possible if we expand the definition of the set joinpoint?
-pete
peter m. murray
pete@xxxxxxxxxxxx
On 9/14/06, Ron Bodkin < rbodkin@xxxxxxxxxxxxxx> wrote:
Hi Peter: the topic of getting old values of a field during set has come up before on the mailing list and as you've determined the only way to do it where you advise different fields is via reflection (e.g., see Matthew Webster's post at http://dev.eclipse.org/mhonarc/lists/aspectj-users/msg04126.html ). I see how the obfuscator might break with reflective code (though I'd hope that an obfuscator wouldn't: lots of libraries now rely on reflection). One idea might be to track the old value of the field also in advice so you can compare the previous value to the current value (e.g., using your map that associates static parts with state).
Hope that helps,
Ron
From: aspectj-users-bounces@xxxxxxxxxxx [mailto: aspectj-users-bounces@xxxxxxxxxxx] On Behalf Of Peter Murray
Sent: Thursday, September 14, 2006 1:23 PM
To: aspectj-users@xxxxxxxxxxx
Subject: Re: [aspectj-users] Question re: declare error
Ron,
Thanks a bunch! That does the trick. I was suspicious that there might be an operator for "subtypes".
Now, the real question is - how can I get ahold of the original value of a field during around set advice so I can use AspectJ to create the ValueChange objects and post them based on the @Transactional annotation. It seems the only way is through reflection which will break once we obfuscate...
Any thoughts on that?
Cheers,
pete
peter m. murray
pete@xxxxxxxxxxxxOn 9/14/06, Ron Bodkin < rbodkin@xxxxxxxxxxxxxx> wrote:Hi Peter,
I would use within(Change+) instead of this(Change). That isn't the exact same semantics as using this (*) but in most cases it would capture your intent: it makes it an error to set the field outside of code that's in a subtype of Change.
(*) it's based on the join points being lexically located inside Change. So it can differ because it won't allow setting the fields in a base class that might be extended by a type that extends Change. It also doesn't allow for setting inside of inter-type declared methods (you could extend the rule to allow those if that matters to you).
From: aspectj-users-bounces@xxxxxxxxxxx [mailto: aspectj-users-bounces@xxxxxxxxxxx] On Behalf Of Peter Murray
Sent: Thursday, September 14, 2006 10:41 AMSubject: Re: [aspectj-users] Question re: declare error
Thanks for your reply, Elizabeth.
That makes sense - do you see a way to accomplish what I am trying to do?
Cheers,
pete
peter m. murray
pete@xxxxxxxxxxxxOn 9/14/06, Echlin Harmer, Elizabeth <echline@xxxxxxx > wrote:Peter
As I understand it, declare is a compile time error or warning; this(), target() and args() are all run time checks. Except in the simplest of cases, it is not possible to tell at compile time what the type of this, target or args will be.Elizabeth
-----Original Message-----
From: aspectj-users-bounces@xxxxxxxxxxx [mailto: aspectj-users-bounces@xxxxxxxxxxx]On Behalf Of Peter Murray
Sent: September 14, 2006 1:12 PM
To: aspectj-users@xxxxxxxxxxx
Subject: [aspectj-users] Question re: declare error
I'd like to declare an error if my @Transactional attributed instance variables are being set outside of the context of a Change object. In other words, I'd like to have an error in this case:
public class Foo
{
@Transactional
String name
public void setName(String newName)
{
name = newName;
}
}
But not in this case:
public class Foo
{
@Transactional
String name
public void setName(String newName)
{
new ValueChange<String>(name, newName)
{
public void set(String value)
{
name = value;
}
}.post();
}
}
It seems like this kind of aspect should do that:
public aspect FieldChangeAspect
{
declare error :
set(@Transactional * *) &&
!this(Change) : "Set of @Transactional variable not in Change object";
}
But this gives me an error saying "this() pointcut designator cannot be used in declare statements." BTW, target(), and args() also give the same error for declare statements i guess, so you can't filter on types of this, target, or args in declares.
Am I missing something? Is there a reason for this or could these be enhancements?
Cheers,
--
-pete
peter m. murray
pete@xxxxxxxxxxxx
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