在 Spring Boot 服务中使用多态性？

Question

In my Spring Boot app, I am thinking of using an approach as the following interface and service implementations:

PDFService:

public interface PDFService {
    String createPdf(UUID uuid);
}

BrandPDFService:

@Service
@RequiredArgsConstructor
public class BrandPDFService implements PDFService {
    
    private final BrandService brandService;

    @Override
    public String createPdf(UUID uuid) {
        Brand brand = brandService.findByUuid(uuid);

        // ... code omitted for brevity

        return generateHtml(brand);
    }
}

ProductPDFService:

@Service
@RequiredArgsConstructor
public class ProductPDFService implements PDFService {

    private final ProductService productService;

    @Override
    public String createPdf(UUID uuid) {
        Product product = productService.findByUuid(uuid);

        // ... code omitted for brevity

        return generateHtml(product);
    }
}

For using these services:

// brand way
PDFService pdfService = new BrandService();
pdfService.createPdf(uuid);


// product way
PDFService pdfService = new ProductService();
pdfService.createPdf(uuid);

So, I think I need to use generic and pass it to PDFService and then their implementations, but I am not sure how to make it properly (using generic or passing via constructor). So, in order to use createPdf efficiently without repeating code (I know I can also use Template Pattern method, but I just wanted to know polymorphism side) how should I apply polymorphism to these Spring Boot Services properly?

Answer 1

Since BrandPDFService and ProductPDFService are Spring beans (because you annotated them with the @Service annotation), you should not be instantiating them yourself by using new . Instead, you should let Spring autowire them into the class where you are using them.

Because they are both implementations of interface PDFService , when you autowire them, you need to have something to let Spring distinguish them. Otherwise, if the field you are autowiring them in is of type PDFService , Spring won't know which implementation of the interface to autowire. You can give the beans names and use the @Qualifier annotation:

@Service("brandPDFService")
public class BrandPDFService implements PDFService { ... }

@Service("productPDFService")
public class ProductPDFService implements PDFService { ... }

// Example controller where you autowire them
@RestController
public class MyController {

    @Autowired
    @Qualifier("brandPDFService")
    private PDFService brandPDFService;

    @Autowired
    @Qualifier("productPDFService")
    private PDFService productPDFService;

    // ...
}

So, I think I need to use generic and pass it to PDFService and then their implementations

I don't know why you think you need to use generics; this doesn't have anything to do with generics.