Annotation member which holds other annotations?

Question

I want to create a custom annotation (using Java) which would accept other annotations as parameter, something like:

public @interface ExclusiveOr {
    Anno         


        

Answer 1

I just ran into this exact problem, but (inspired by @ivan_ivanovich_ivanoff) I have discovered a way to specify a bundle of any combination of Annotations as an annotation member: use a prototype / template class.

In this example I define a WhereOr (i.e. a "where clause" for my model annotation) which I need to contain arbitrary Spring meta-annotations (like @Qualifier meta-annotations).

The minor (?) defect in this is the forced dereferencing that separates the implementation of the where clause with the concrete type that it describes.

@Target({})
@Retention(RetentionPolicy.RUNTIME)
public @interface WhereOr {
    Class[] value() default {};
}

@Target({ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface JsonModel {
    Class value();
    WhereOr where() default @WhereOr;
}

public class Prototypes {
    @Qualifier("myContext")
    @PreAuthorize("hasRole('ROLE_ADMINISTRATOR')")
    public static class ExampleAnd {
    }
}

@JsonModel(
        value = MusicLibrary.class,
        where = @WhereOr(Prototypes.ExampleAnd.class)
)
public interface JsonMusicLibrary {
    @JsonIgnore
    int getMajorVersion();
    // ...
}

I will programmatically extract the possible valid configurations from the "where clause" annotation. In this case I also use the prototypes class as a logical AND grouping and the array of classes as the logical OR.