Custom Annotation Processing

[sotretus]

Hi,

I would like to be able to annotate my services with a custom annotation, and run some AOP-like code only on those methods. I know I can do this with standard AOP and @Apsect annotations, but instead of defining in the aspect itself (or xml) which methods will be intercepted, I want to define it in every method I need, to have more visibility when coding and reviewing/code maintenance.

An example would be to perform some lock checking on specific methods. I would like to do the following

@Lockable
public void performBankTransaction(....)

And because that method is annotated with @Lockable, execute some code before it (that would lock based on some condition).

As a super bonus, I would also like to be able to annotate a parameter in the method to control concurrency, like so:

@Lockable
public void performBankTransaction(@LockId Account from, Account to)

would lock on the method using the 'from' field only (and my code knows how to lock based on that).

I tried doing some searches for this but I'm having a hard time figuring out the correct keywords, as "annotations" / custom AOP etc lead me to all the standard pages.

Any help would be much appreciated
Thanks in advance
AB

[ramnivas]

This should be really easy to implement. You need a pointcut such as:

execution(@com.myco.Loackable * *(..))

and advise it to perform the locking logic.

-Ramnivas

[sotretus]

Thanks! that seems pretty easy, I thought I needed to do some pointcut based on interface name (like *Service) which I didn't particularly like. This is exactly what I wanted.

Is there any way to get the @LockId parameter annotation inside the interceptor? (I want the instance object that has that annotation).

Thanks in advance,
AB

[ramnivas]

Getting the argument with @LockId requires the use of reflection. You will need code such as the following:

@Before("lockOperation()")
public void lock(JoinPoint jp) {
   Method m = ((MethodSignature)jp).getMethod();
   Annotation[][] paramAnnots = m.getParameterAnnotations();
   ... now check which paramAnnot is @LockId, 
   ... that will give you the index, 
   ... then grab the parameter by jp.getArgs()[index]
}

-Ramnivas

[sotretus]

Sounds Perfect. I will try it and let the forum know.

Sincerely,
AB

[sotretus]

Apparently I cannot cast the JoinPoint to the MethodSignature interface. I've debugged the code and I'm getting a MethodInvocationProceedingJoinPoint which only implements the ProceedingJoinPoint, JoinPoint.StaticPart interfaces, none of which extends MethodSignature.

The exact error is
java.lang.ClassCastException: org.springframework.aop.aspectj.MethodInvocationPr oceedingJoinPoint cannot be cast to org.aspectj.lang.reflect.MethodSignature

I've been looking at available methods and I cannot find any other that can be used to get the Method class (or actually the @Annotation used in the class).

As always any help is much appreciated
Regards
AB

[ramnivas]

I missed getSignagure().. try the following:

Method m = ((MethodSignature)jp.getSignature()).getMethod();

-Ramnivas

[sotretus]

Worked like a charm, silly me.

The only issue I had is that this method is an implementation of an interface method, and I'm getting the interface's Method class instead of the implementation ones.

I eventually did something like this (with pretty formatting)

jp.getTarget().getClass().getMethod(m.getName(), m.getParameterTypes())

Thanks for all your help pal
Regards
AB