@Async``@Service独立的Spring Boot应用程序中带注释的类中的方法不会异步运行。我究竟做错了什么？

当我直接从主类（带@SpringBootApplication注释）运行相同的方法时，它可以工作。例：

主班

@SpringBootApplication
@EnableAsync
public class Application implements CommandLineRunner {

    @Override
    public void run(String... args) throws Exception {
        // here when I call downloadAnSave() it runs asynchronously...
        // but when I call downloadAnSave() via downloadAllImages() it does not run asynchronously...
    }

}

和我的 服务类 （这里的异步行为不起作用）：

@EnableAsync
@Service
public class ImageProcessorService implements IIMageProcessorService {

    public void downloadAllImages(Run lastRun) {
        // this method calls downloadAnSave() in loop and should run asynchronously....
    }

    @Async
    @Override
    public boolean downloadAnSave(String productId, String imageUrl) {
        //
    }

}