The bean of the DataServiceImpl class needs to be injected into that of the BusinessServiceImpl class.

We can do that by specifying an @Autowired annotation in the instance variable of the DataService interface in the BusinessServiceImpl class:

    @Service
    public class BusinessServiceImpl { 

      @Autowired 
      private DataService dataService;

Now that we have defined the beans and their wiring, to test this, we need an implementation of DataService. We will create a simple, hardcoded implementation. DataServiceImpl returns a couple of pieces of data:

    @Repository 
    public class DataServiceImpl implements DataService { 

      public List<Data> retrieveData(User user) { 
        return Arrays.asList(new Data(10), new Data(20)); 
      } 
    }

Now that we have our beans and dependencies defined, let's focus on how to create and run a Spring IoC container.