jersey2-guice-impl/src/main/java/com/squarespace/jersey2/guice/BindingUtils.java
public static <T> Set<Annotation> getQualifiers(Key<T> key) {
    Annotation annotation = key.getAnnotation();
    if (annotation != null) {
      
      // Replace 'com.google.inject.name.Named' with 'javax.inject.Named' 
      if (annotation instanceof com.google.inject.name.Named) {
        annotation = toThreeThirtyNamed((com.google.inject.name.Named)annotation);
      }
      
      Class<? extends Annotation> type = annotation.annotationType();
      if (type.isAnnotationPresent(Qualifier.class)) {
        return Collections.singleton(annotation);
      }
      
      return Collections.<Annotation>singleton(new GuiceQualifier<>(key));
    }
    
    Class<? extends Annotation> annotationType = key.getAnnotationType();
    if (annotationType != null) {
      return Collections.<Annotation>singleton(new GuiceQualifier<>(key));
    }
    
    return Collections.emptySet();
  }
public static <T> Set<Annotation> getQualifiers(Key<T> key) {
    Annotation annotation = key.getAnnotation();
    if (annotation != null) {
      
      // Replace 'com.google.inject.name.Named' with 'javax.inject.Named' 
      if (annotation instanceof com.google.inject.name.Named) {
        annotation = toThreeThirtyNamed((com.google.inject.name.Named)annotation);
      }
      
      Class<? extends Annotation> type = annotation.annotationType();
      if (type.isAnnotationPresent(Qualifier.class)) {
        return Collections.singleton(annotation);
      }
      
      return Collections.<Annotation>singleton(new GuiceQualifier<>(key));
    }
    
    Class<? extends Annotation> annotationType = key.getAnnotationType();
    if (annotationType != null) {
      return Collections.<Annotation>singleton(new GuiceQualifier<>(key));
    }
    
    return Collections.emptySet();
  }
Returns a {@link Set} of qualifier {@link Annotation}s for
the given {@link Key}.

NOTE: The {@link Set} will be either empty or will have
at most one {@link Annotation} in it.