Question

I’m trying to create a simple web-page, which is displaying the data, received from web-service

@Service
@Transactional
public class TopicService {
    @Autowired
    private TopicRepository topicRepository;

    public int saveTopic(Topic topic){
        return topicRepository.save(topic).getId();

        }

    public Iterable<Topic> findAllTopics(){
        return topicRepository.findAll();

    }

    public Topic findTopicByID(Long id){
        return topicRepository.findOne(id);
    }

    public List<Topic> findTopicsByTag(Tag tag){
        return topicRepository.findAllByTopicTag(tag);
    }

}

topic repository extends CRUD-repository

@Repository
public interface TopicRepository extends CrudRepository<Topic, Long>
{
    List<Topic> findAllByTopicTag(Tag currentTag);

} 

the controller invokes a service in the following way

@Controller
public class HomeController {

    private TopicService service;

    private static final Logger logger = LoggerFactory.getLogger(HomeController.class);

    @RequestMapping(value = "/", method = RequestMethod.GET)
    public ModelAndView home(Locale locale, Model model) 
    {
         Iterable<Topic> listTopic = service.findAllTopics();
         return new ModelAndView("home", "model", listTopic);
}
}

this string

Iterable listTopic = service.findAllTopics();

throws null-pointer exception. I guess, because the service isn’t initialized. How could I perform correct initialization of the service?

Answer 1

You need to autowire the TopicService in HomeController:

@Controller
public class HomeController {

    @Aurowired
    private TopicService service;