[hibernate-dev] Accessing annotation properties values

[Emmanuel Bernard]

Because the set of annotations is well defined, I won't if you could use an actual real implementation instead of a proxy. That's mor work but this will be much faster as we would not need to build the proxy. 
Alternatively, I wonder if we could cache the serialized proxy somewhere or even build it at compile time and bundle it in the jar. 

Emmanuel

On 4 oct. 2012, at 09:01, Łukasz Antoniak <lukasz.antoniak at gmail.com> wrote:

> Hello Team,
> 
> In Envers code we use ReflactionManager and XProperty#getAnnotation(Class<T>) quite often. While working on metamodel branch, I 
> have started replacing all those calls with JandexHelper#getValue(AnnotationInstance, String, Class<T>) method. The code became 
> less type safe and grew in size. The only solution that comes to my mind is to create annotation proxy that directs calls to 
> underlying AnnotationInstance. Something like:
> public static <T> T createAnnotationProxy(final AnnotationInstance annotationInstance, final Class<T> annotation) {
>    try {
>        final ProxyFactory proxyFactory = new ProxyFactory();
>        proxyFactory.setInterfaces( new Class[] { annotation.getClassLoader().loadClass( annotation.getName() ) } );
>        final Class proxyClass = proxyFactory.createClass();
>        final ProxyObject proxyObject = (ProxyObject) proxyClass.newInstance();
>        proxyObject.setHandler( new MethodHandler() {
>            @Override
>            public Object invoke(Object self, Method thisMethod, Method proceed, Object[] args) throws Throwable {
>                String executedMethodName = thisMethod.getName();
>                if ( "toString".equals( executedMethodName ) ) {
>                    return proxyClass.getName() + "@" + System.identityHashCode( self );
>                }
>                return JandexHelper.getValue( annotationInstance, executedMethodName, Object.class );
>            }
>        } );
>        return (T) proxyObject;
>    }
>    catch ( Exception e ) {
>        throw new HibernateException( e );
>    }
> }
> 
> This allows to:
> Audited audited = createAnnotationProxy( auditedAnnotationInstance, Audited.class );
> ModificationStore modStore = audited.modStore();
> RelationTargetAuditMode relationTarget = audited.targetAuditMode();
> 
> I have initially shown the above implementation to Hardy and we were wondering what you all think of this approach. Of course 
> executing such method increases memory usage and decreases performance, but from design point of view, I can think of situations 
> where it fits.
> 
> Regards,
> Lukasz
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