static Object invokeValueMethod(Annotation a) {
        try {
            final Method method = Iterables.getFirst(getMethods(a.annotationType(), withName("value")), null);
            assert method != null : "No 'value' method is found from " + a;
            return method.invoke(a);
        } catch (Exception e) {
            throw new IllegalStateException("An annotation @" + a.annotationType().getSimpleName() +
                                            " must have a 'value' method", e);
        }
    }
Returns an object which is returned by {@code value()} method of the specified annotation {@code a}.
core/src/main/java/com/linecorp/armeria/internal/server/annotation/AnnotatedObjectFactory.java