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RE: [aspectj-users] set() capture oldvalue
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This is a reasonable requirement. There are some potential complications
in the implementation to support after advice, and the interface to
provide access to the "before" value at a set join point is a little
awkward: it really has to go on the JoinPoint interface alongside getThis,
getTarget, and getArgs, even though it only applies to set join points.
If we did something like that you could write:
after(Object newValue) returning : set( * *) && args(newValue) { // the
pointcut would obviously be refined for a 'real' application...
Object oldValue =
thisJoinPoint.getOriginalFieldValueAtAFieldSetJoinPoint() ; // would need
a better name...
if (!oldValue.equals(newValue) {
firePropertyChangeEvent(oldValue,newValue,thisJoinPoint.getSignature());
}
}
Please raise an enhancement request on bugzilla if you think something
like this would be useful, and then I encourage others who have opinions
(for or against) to comment there.
-- Adrian
Adrian_Colyer@xxxxxxxxxx
"Nitzan Volman" <nitzan@xxxxxxxxxxx>
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17/05/2005 15:34
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RE: [aspectj-users] set() capture oldvalue
Hi,
I encountered the same problem, and I think what Tim suggested is needed
in the language.
My use case is simple: I am trying to audit changes to an object by
monitoring field modifications, on each field modification (set operation)
I need to compare the previous and value of the field with the new value
to make sure the value really changed, no point in auditing fields that
are reset to the same value.
A typical scenario where this happens is when you submit web forms, most
of the values are the same but the "set" is called anyway.
I can think of several solutions for this use case that would not require
adding a feature to AspectJ... But doing this using AspectJ would be a
great enhancement
/Nitzan Volman
-----Original Message-----
From: aspectj-users-bounces@xxxxxxxxxxx
[mailto:aspectj-users-bounces@xxxxxxxxxxx] On Behalf Of Tim Schafer
Sent: Monday, May 16, 2005 5:39 PM
To: aspectj-users@xxxxxxxxxxx
Subject: Re: [aspectj-users] set() capture oldvalue
It's true in this particular application, the performance of reflection
won't
kill the application.
But it's just something that I feel is missing from the language. I wanted
to see what other use cases might exist. Performance could be a problem in
some cases.
Tim Schafer
tschafer@xxxxxxxxxxx
----Original Message Follows----
From: Matthew Webster <matthew_webster@xxxxxxxxxx>
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Subject: Re: [aspectj-users] set() capture oldvalue
Date: Mon, 16 May 2005 07:50:11 +0100
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Tim,
If you have a concern about the performance of something measure it. Many
frameworks use performance. I don't believe it's impact on overall
application performance will be as bad as you think.
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/
"Tim Schafer" <tschafer@xxxxxxxxxxx>@eclipse.org on 13/05/2005 19:11:36
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Subject: Re: [aspectj-users] set() capture oldvalue
That's exactly what I'm doing.
Using reflection.
I'm concerned about performance.
If I were using aspects I wouldn't use refelection in each setter to get
the old value. The aspect compiler should be able to do this work for me.
I believe it's a major defeciency that this isn't avaiblable. Are there
already plans to fix this? Should I file a bug?
Tim Schafer
tschafer@xxxxxxxxxxx
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Tim,
I'm sure there was a thread on either aspectj-users or aspectj-dev but I
can't find it. Bottom line is the existing field value is not a property
of the join point so you must get it directly. The simple examples below
shows you how to use reflection or direct access:
public class SomeClass {
private int intField;
public void setInt (int i) {
intField = i;
}
}
public aspect Aspect {
pointcut fieldSet(int newValue) :
set(* SomeClass+.*) && args(newValue)
&& withincode(* SomeClass+.set*(..))
;
before (int newValue) : fieldSet (newValue) {
Object oldValue = null;
try {
Class clazz =
thisJoinPoint.getSignature().getDeclaringType();
String fieldName =
thisJoinPoint.getSignature().getName();
Field field = clazz.getDeclaredField(fieldName);
field.setAccessible(true);
oldValue = field.get(thisJoinPoint.getThis());
}
catch (Exception ex) {
ex.printStackTrace();
}
System.out.println("? beforeFieldSet() oldVaue=" + oldValue
+ ", newValue=" + newValue);
}
}
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);
}
}
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/
"Tim Schafer" <tschafer@xxxxxxxxxxx>@eclipse.org on 11/05/2005 21:47:44
Please respond to aspectj-users@xxxxxxxxxxx
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Subject: [aspectj-users] set() capture oldvalue
I've used the following pointcut to capture all field modifications that
occur within a setter method.
pointcut fieldSet(Object newValue) : set(* SomeClass+.*) && args(newValue)
&& withincode(* SomeClass+.set*(..));
I can capture the new value, but I can't capture the old value without
resorting to reflection. In theory aspectJ could provide access to the old
value more statically. But aspectJ doesn't seem to support this. Or am I
missing something?
Tim Schafer
tschafer@xxxxxxxxxxx
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