Question

I wanna learn and have fun with annotations. Here is my use case: I have got a bunch of classes who basically have the same role: validate a video URL against a regex (1 method) and return the corresponding embedded HTML (another method).

The thing is the validation method is always the same. I could of course use inheritance, but I would like if it is possible to create an annotation like this:

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.??)
@Inherited
@Documented
public @interface VideoProvider {
        String regex();
        int group() default 1;
}

Processed like that:

//processor class
public boolean process(Set<? extends TypeElement> annotations,
        RoundEnvironment roundEnv) {
    for (TypeElement annotation : annotations) {
        for (Element e :    roundEnv.getElementsAnnotatedWith(annotation)) {
            if (e.getKind().isClass()) {
                //?????
            }
        }
    }
    return false;
}

The idea would be to dynamically change the annotated classes to inject a method that performs the validation.
Is that feasible ?

Thanks in advance!

Rolf

Answer 1

Look at using java’s Proxy class you cglib Enhancer class. Both solutions allow you to proxy a class and over take any method.