Spring Components

Controller

• Handle HTTP methods
• Keep them as simple as possible
• @RestController is a child of @Controller
• @RestController automatically converts json to pojo

@Controller
@RequestMapping("/customer") // Handles any method, GET, POST, PATCH, etc
public class CustomerController {

  @Autowired
  private CustomerDAO customerDAO; // scans all components that implements this interface and picks the first

  // @RequestMapping(path="/list",method=RequestMethod.GET)
  @GetMapping("/list")
  public String listCustomers(Model model) {
    List<Customer> customers = customerDAO.getCustomers();
    model.addAttribute("customers", customers); // model for display
    return "list-customers";
  }
}

Service

• Service Facade design pattern
• Intermediate layer for custom business logic
• Integrate data from multiple sources (DAO/repositories)
• It's a good practice to start and commit transactions on the service layer

public interface CustomerService {
  public List<Customer> getCustomers();

  public void saveCustomer(Customer customer);
}

@Service
public class CustomerServiceImpl implements CustomerService {

  @Autowired
  private CustomerDAO customerDAO; // scans all components that implements this interface and picks the first

  @Override
  @Transactional // Automatically starts and commits transactions)
  public List<Customer> getCustomers() {
    return customerDAO.getCustomers();
  }

  @Override
  @Transactional
  public void saveCustomer(Customer customer) {
    customerDAO.saveCustomer(customer);
  }
}

Repository

• Data Access Object (DAO) is a design pattern responsible for interfacing with the database
• It's a helper class to talk to the database
• DAO classes are annotated with @Repository

public interface CustomerDAO {
  public List<Customer> getCustomers();
}

@Repository
public class CustomerDAOImpl implements CustomerDAO {

  @Autowired // inject dependency
  private SessionFactory sessionFactory;

  @Override
  @Transactional // Automatically starts and commits transactions
  public List<Customer> getCustomers() {
    Session session = sessionFactory.getCurrentSession();
    Query<Customer> query = session.createQuery("from Customer", Customer.class);
    List<Customer> customers = query.getResultList();
    return customers;
  }
}