How to call method from a reference send to annotation in java

Question

I have a Interface I and a Abstract Class A , I have My custom annotation MyAnnotation which should take parameter as subclass S of A, now while processing annotation I want to call method of concrete class S

public interface I{
   void m1();
}

public abstract class A implements I {
    public abstract void m1();
}

public @interface MyAnnotation {
    public Class< ? extends A> ref();
    public Class< ? super A> ref2();
}

public S extends A{
    public void m1() {}
}

I am annotating method like

@MyAnnotation(ref= new XX() )  or @MyAnnotation(ref= XX.class )
@MyAnnotation(ref= new yy() ) or @MyAnnotation(ref= yy.class )

whichever works

//In spring aspect before processing I am getting method annotation and trying to call m1()  
annotation.ref().m1() //Error
annotation.ref2().m1() //Error

abstarct and public S extends A aren't correct

Andrew
– Andrew

2018-10-07 17:17:39 +00:00
Commented Oct 7, 2018 at 17:17 — Andrew
– Andrew, Commented Oct 7, 2018 at 17:17

Michael · Accepted Answer · 2018-10-07 18:23:56Z

3

You can't use new XX() in an annotation. Annotations parameters can use a very specific set of types:

primitive

String

Class

an Enum

another Annotation

an array of any of the above

See this answer.

So to accomplish what you're trying to accomplish, you'd have to use a class.

You would then have to use reflection to create an instance and invoke the method.

Class<?> clazz = annotation.ref();
I instance = (I) cls.getConstructor().newInstance();
instance.m1();

See this answer.

Your classes must all have no-argument constructors, else you'll only be able to instantiate some this way but not others (leading you to have to conditionally branch based on the class).

edited Oct 7, 2018 at 18:23

answered Oct 7, 2018 at 17:33

Michael

44.5k12 gold badges97 silver badges143 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

ernest_k Over a year ago

I think ((I) cls.newInstance()).m1() is a better option than ...getMethod(...).invoke(...)

Eugene Over a year ago

@ernest_k newInstance is deprecated since 9; it's better to call Constructor::newInstance

ernest_k Over a year ago

@Eugene That's right. My comment is just about avoiding the getMethod(...).invoke(...) part, if you notice...

Michael Over a year ago

@ernest_k + Eugene, You're both right. It was a bit of a lazy answer, mostly just copied and pasted from the sources I listed. I've improved it now

Mariusz.v7 · Accepted Answer · 2018-10-07 17:20:34Z

0

You can't do that simply like that. You need an instance of the class first. If your A class is a Spring's bean, you can inject ApplicationContext and get the bean from there. Then you can call a method.

@Autowired
private ApplicationContext context;

void test(MyAnnotation annotation) {
    A bean = context.getBean(annotation.ref());
    bean.m1();
}

answered Oct 7, 2018 at 17:20

Mariusz.v7

2,4622 gold badges20 silver badges28 bronze badges

Collectives™ on Stack Overflow

How to call method from a reference send to annotation in java

2 Answers 2

4 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related