Spring 引导/数据：用于 crud 操作的通用服务 class

Question

Let's say I want to create a REST API which performs basic CRUD operations on several entities. For that I've created generic interface:

public interface CrudService<T>{
    //generic CRUD methods
}

And its implementation for Foo entity:

@Entity
public class Foo {
}

@Repository
public interface FooRepository extends JpaRepository<Foo, Long>{
}

@Service
@Transactional
public class FooCrudServiceImpl implements CrudService{

    @Autowired
    private FooRepository repository;

    //CRUD methods implementation
}

@RestController
class FooController{
    @Autowired
    private CrudService<Foo> crudService;

    //Controller methods
}

What I want to avoid now is creating service implementation for each entity with basically the same logic. So I tried to create a generic service class which can be called from multiple controllers(FooController, BarController etc.):

@Service
@Transactional
class GenericCrudServiceImpl<T> implements CrudService{

    @Autowired
    private JpaRepository<T, Long> repository;

    //generic CRUD methods implementation
}

and pass that service class to each controller where the entity type would be specified. The problem is that there will be multiple repository beans that could be injected into GenericCrudServiceImpl (FooRepository, BarRepository etc.) and just by specifying the type of JpaRepository Spring still doesn't know which bean to inject. I don't want to call repository beans directly from controller classes to maintain seperation of responsibilities.

Additionally, for some reason this problem doesn't occur on controller level where I inject CrudService interface and Spring understands which bean should it choose, which messes with my whole understanding of dependency injection.

Is there a way to create such a generic service class? Other posts on stackoverflow didn't provide me with an answer.

Bonus question: what's the difference between using a @Qualifier annotation and injecting a specific implementation (in this example FooCrudServiceImpl instead of CrudService in controller class)? In both cases pointing to different use implementation requires changing one line of code.

Answer 1

What about that:

@Transactional
public class GenericCrudServiceImpl<T> implements CrudService{
   private JpaRepository<T, Long> repository;

   public GenericCrudServiceImpl(JpaRepository<T, Long> repository) {
      this.repository = repository;
   }
}

And Spring configuration:

@Configuration
public PersistanceConfiguration {
   @Bean
   public JpaRepository<Foo, Long> fooJpaRepository() {
      ...
   }

   @Bean
   public JpaRepository<Foo, Long> booJpaRepository() {
      ...
   }

   @Bean
   public CrudService<Foo> fooService(JpaRepository<Foo, Long> fooJpaRepository) {
      return new GenericCrudServiceImpl(fooJpaRepository);
   }

   @Bean
   public CrudService<Foo> booService(JpaRepository<Foo, Long> booJpaRepository) {
      return new GenericCrudServiceImpl(booJpaRepository);
   }
}

And Controller

@RestController
class FooController{
       
   // Injection by bean name 'fooService'
   @Autowired
   private CrudService<Foo> fooService;
    
   //Controller methods
}