从实体访问存储库或服务

Question

I'm using Spring Boot to write server application.

Most of the time, I write all business logic inside services, where I use @Autowired to access repositories and other services.

However, sometimes I want to access certain service or property from @Entity class, which cannot use @Autowired .

For instance, I have an entity that should be able to serialize itself to JSON. In JSON, it should have imageUrl field, which contains of image name (stored in database and as a property in the @Entity class) and base url, which is only available in application.properties. This means that I have to use @Value annotation inside @Entity class, but it doesn't work that way.

So I create a service which looks like this:

@Service
public class FilesService {

    private static FilesService instance;

    @PostConstruct
    public void init() {
        FilesService.instance = this;
    }

    public static FilesService getInstance() {
        return instance;
    }

    @Value("${files.path}")
    String filesPath;
    @Value("${files.url}")
    String filesUrl;

    public String saveFile(MultipartFile file) throws IOException {
        if (file == null || file.isEmpty()) {
            return null;
        }
        String filename = UUID.randomUUID().toString();
        file.transferTo(new File(filesPath + filename));
        return filename;
    }

    public String getFileUrl(String filename) {
        if (filename == null || filename.length() == 0) {
            return null;
        }
        return filesUrl + filename;
    }

}

And then inside the @Entity class I write the following code:

@JsonProperty
public String getImageUrl() {
    return FilesService.getInstance().getFileUrl(imageName);
}

This works, but it doesn't look right. Moreover, I concern whether this can lead to some side effects if used with less trivial @Service classes or @Repository classes.

What is the correct way to use @Repository and @Service classes from @Entity classes or any other non- @Component classes (classes not managed by Spring)?

Answer 1

Well, I'd say there's no correct way of using repositories and services from entities since every fiber of my being screams of wrongness but that being said , you can refer to this link for suggestions on how to do it.

In your case, I think it should allow you to populate @Value fields within your entities, which would actually be preferable to autowiring the service.