How to decide constraint validator class at runtime?

Question

I have defined an annotation for validation like this:

@Documented
@Constraint(validatedBy = MyValidator.class)
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)

public @interface MyCustomValid {
 //required methods
}

Now, I want to decide the "validatedBy" class at runtime. Like I have a field in my class:

public class MyClass {
      @MyCustomValid
      MyObject myObject;
}

How do I pass the ConstraintValidator class at runtime. I have different implementations for different cases.

Answer 1

Annotations are compiled into the code at compile time and they can't change, so you need a hack.

Create a validation class which delegates to another validator. The delegate needs to be created at runtime, using whatever algorithm you design. Note that the code might be used concurrently, so you need a thread-safe initialization.