public interface ConstraintValidator<A extends Annotation, T> {

    default void initialize(A constraintAnnotation) { }

    default boolean isValid(T value, ConstraintValidatorContext context) {
        return isValid(value);
    }

    //TODO breaks backward compatibility by adding a new method to ConstraintValidator
    boolean isValid(T value);
}



public interface ConstraintValidatorFactory {
    <T extends ConstraintValidator<?, ?>> T getInstance(Class<T> key);
    void releaseInstance(ConstraintValidator<?, ?> instance);
    
    // enlist a new validator for a given constraint programmatically
    <A extends Annotation> void register(Class<A> annotation, ConstraintValidator<A,?> validator);
    // resolve validator for a given annotation
    // TODO: to fully resolve, one need the actual return or parameter type as there can be several validators per constraint annotation
    <A extends Annotation> ConstraintValidator<? extends Annotation, ?> resolve(Class<A> annotation);
}

ConstraintValidatorFactory cvf = factory.getConstraintValidatorFactory();
cvf.register(Directory.class, (ConstraintValidator<Directory, File) File::isDirectory);
cvf.register(Writable.class, (ConstraintValidator<Writable, File) File::canWrite);