The document discusses various techniques for refactoring code based on domain-driven design principles, including protecting invariants by adding validation logic, using subclasses to represent different types of objects and encapsulating state changes, encapsulating operations within objects through methods, and applying the specification pattern to represent business rules and allow flexible querying of objects. It provides examples of refactoring customer and order domain code using these techniques, and testing the refactored code to ensure correctness is maintained.

1. REFACTORING CODE
DOMAIN DRIVEN DESIGN WAY
Supported By:

2. Supported By:
I’M ANDI PANGERAN
@andi_pangeran
cybercoding.wordpress.com

3. Supported By:
AGENDA
 PRACTICE HOW TO REFACTORING CODE BASED ON DOMAIN
DRIVEN DESIGN MINDSET
 PRACTICE HOW TO WRITE UNIT TESTING

4. Supported By:
JOKO
Individual who has significant expertise in the
domain of the system being developed.
DOMAIN EXPERT
MEET OUR ACTOR

5. Supported By:
BENTO
Individual who has spend all of his life for coding.
PROGRAMMER
MEET OUR ACTOR

6. Supported By:
PRACTICE

7. Supported By:
Protect your invariants
REFACTORING

8. Supported By:
JOKO
PRACTICE
“A customer must
always have an
email address.”

9. Supported By:
PRACTICE
BENTO
public class Customer {
private String email;
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}

10. Supported By:
PRACTICE
BENTO
public class CostumerTest {
@Test
public void should_always_have_an_email() {
Customer customer = new Customer();
assertEquals(customer.getEmail(), "andi.pangeran@jtravl.com");
}
}
TEST FAIL

11. Supported By:
PRACTICE
BENTO
public class CostumerTest {
@Test
public void should_always_have_an_email() {
Customer customer = new Customer();
customer.setEmail("andi.pangeran@jtravl.com");
assertEquals(customer.getEmail(), "andi.pangeran@jtravl.com");
}
}
TEST PASSED

12. Supported By:
PRACTICE
BENTO
public class Customer {
private String email;
public Customer(String email) {
this.email = email;
}
}

13. Supported By:
PRACTICE
BENTO
public class CostumerTest {
@Test
public void should_always_have_an_email() {
Customer customer = new Customer("andi.pangeran@jtravl.com");
assertEquals(customer.getEmail(), "andi.pangeran@jtravl.com");
}
}
TEST PASSED

14. Supported By:
Use object as concistency boundaries
REFACTORING

15. Supported By:
JOKO
PRACTICE
“later prospective customer can be
upgraded to paying customer“
“Paying customer must have phone
number”
“we have two type of customer,
prospective and paying customer.”

16. Supported By:
PRACTICE
BENTO
public class ProspectiveCustomer extends Customer {
/* other attribute */
}
public class PayingCustomer extends Customer {
/* other attribute */
private String phone;
public PayingCustomer(String email, String phone) {
super(email);
this.phone = phone;
}
}

17. Supported By:
PRACTICE
BENTO
@Test
public void upgraded_prospective_paying() {
ProspectiveCustomer pcustomer = new
ProspectiveCustomer("andi.pangeran@jtravl.com");
assertEquals(pcustomer.getEmail(), "andi.pangeran@jtravl.com");
PayingCustomer payCustomer =
new PayingCustomer(pcustomer.getName(), “0852xxx”);
assertEquals(payCustomer.getEmail(), "andi.pangeran@jtravl.com");
assertEquals(payCustomer.getPhone(), " 0852xxx");
}
TEST FAIL

18. Supported By:
PRACTICE
BENTO
@Test
public void upgraded_prospective_paying() {
ProspectiveCustomer pcustomer = new
ProspectiveCustomer("andi.pangeran@jtravl.com");
assertEquals(pcustomer.getEmail(), "andi.pangeran@jtravl.com");
PayingCustomer payCustomer =
new PayingCustomer(pcustomer.getEmail(), “0852xxx”);
assertEquals(payCustomer.getEmail(), "andi.pangeran@jtravl.com");
assertEquals(payCustomer.getPhone(), " 0852xxx");
}
TEST PASSED

19. Supported By:
PRACTICE
BENTO
public class ProspectiveCustomer extends Customer {
/* other attribute */
public PayingCustomer upgradeToPayingCustomer(String phone) {
return new PayingCustomer(this.email, phone);
}
}
public class PayingCustomer extends Customer {
/* other attribute */
private String phone;
public PayingCustomer(String email, String phone) {
super(email);
this.phone = phone;
}
}

20. Supported By:
PRACTICE
BENTO
@Test
public void upgraded_prospective_paying() {
ProspectiveCustomer pcustomer = new
ProspectiveCustomer("andi.pangeran@jtravl.com");
assertEquals(pcustomer.getEmail(), "andi.pangeran@jtravl.com");
PayingCustomer payCustomer = pcostumer.upgradeToPaying(“0852xxx”);
assertEquals(payCustomer.getEmail(), "andi.pangeran@jtravl.com");
assertEquals(payCustomer.getPhone(), " 0852xxx");
}
TEST PASSED

21. Supported By:
JOKO
PRACTICE
“Paying customer must always have a
valid phone number”

22. Supported By:
PRACTICE
BENTO
@Test
public void upgraded_prospective_paying() {
PayingCustomer payCustomer =
new PayingCustomer(“test@mail.com", “badphonenumber”);
exception.expect(IllegalArgumentException.class);
}
TEST FAIL

23. Supported By:
PRACTICE
BENTO
public class PayingCustomer extends Customer {
/* other attribute */
private String phone;
public PayingCustomer(String email, String phone) {
super(email);
if (/* validation stuff of phone*/ ) {
throw new IllegalArgumentException();
}
this.phone = phone;
}
}
TEST PASSED

24. Supported By:
PRACTICE
BENTO
public class PayingCustomer extends Customer {
/* other attribute */
private String phone;
public PayingCustomer(String email, String phone) {
super(email);
if (/* validation stuff of phone*/ ) {
throw new IllegalArgumentException();
}
this.phone = phone;
}
}
TEST PASSED

25. Supported By:
Encapulate state and behavior with
value object
REFACTORING

26. Supported By:
PRACTICE
 Intro to value object
 Intro to immutable object

27. Supported By:
PRACTICE
BENTO
public class PhoneNumber {
private final String phone;
public PhoneNumber(String phone) {
if (/* validation stuff of phone*/ ) {
throw new IllegalArgumentException();
}
this.phone = phone;
}
public String getPhone() {
{
return this.phone;
}
}

28. Supported By:
PRACTICE
BENTO
public class PayingCustomer extends Customer {
/* other attribute */
private PhoneNumber phone;
public PayingCustomer(String email, PhoneNumber phone) {
super(email);
this.phone = phone;
}
}
TEST PASSED

29. Supported By:
PRACTICE
BENTO
@Test
public void upgraded_prospective_paying() {
PayingCustomer payCustomer =
new PayingCustomer(“test@mail.com", new
PhoneNumber(“badphonenumber”));
exception.expect(IllegalArgumentException.class);
}
TEST PASSED

30. Supported By:
Encapulate Operations
REFACTORING

31. Supported By:
JOKO
PRACTICE
“a Customer orders product and pays for
them”

32. Supported By:
Service.create
BENTO
Order order = new Order();
order.setCustomer(customer);
order.setProducts(products);
order.setStatus(PAYMENTSTATUS.UNPAID);
order.setPaidAmount(500);
order.setPaidCurrency(CURRENCY.IDR);
order.setStatus(PAYMENTSTATUS.PAID);
PRACTICE
Service.pay

33. Supported By:
Service.create
BENTO
Order order = new Order();
order.setCustomer(customer);
order.setProducts(products);
order.setStatus(new PaymentStatus(PAYMENTSTATUS.UNPAID));
order.setPaidAmount(500);
order.setPaidCurrency(CURRENCY.IDR);
order.setStatus(new PaymentStatus(PAYMENTSTATUS.PAID));
PRACTICE
Service.pay

34. Supported By:
Service.create
BENTO
Order order = new Order();
order.setCustomer(customer);
order.setProducts(products);
order.setStatus(new PaymentStatus(PAYMENTSTATUS.UNPAID));
order.setPaidMonetary(new Money(500, CURRENCY.IDR));
order.setStatus(new PaymentStatus(PAYMENTSTATUS.PAID));
PRACTICE
Service.pay

35. Supported By:
Service.create
BENTO
Order order = new Order(customer, products);
//set payment status in order constructor
order.setPaidMonetary(new Money(500, CURRENCY.IDR));
order.setStatus(new PaymentStatus(PAYMENTSTATUS.PAID));
PRACTICE
Service.pay

36. Supported By:
Service.create
BENTO
Order order = new Order(customer, products);
//set payment status in order constructor
order.pay (new Money(500, CURRENCY.IDR));
//set payment status in pay procedure
PRACTICE
Service.pay

37. Supported By:
Use Spefication
REFACTORING

38. Supported By:
JOKO
PRACTICE
“premium customers get special offers”

39. Supported By:
Service.premium
BENTO
If (customer.isPremium()) {
//send offer
}
PRACTICE

40. Supported By:
JOKO
PRACTICE
“order 3 times to become premium
customer”

41. Supported By:
Specification Interface
BENTO
public interface Specification<T> {
boolean isSatisfiedBy(T t);
Class<T> getType();
}
PRACTICE
Specification Abstract
abstract public class AbstractSpecification<T> implements
Specification<T> {
@Override
public boolean isSatisfiedBy(T t) {
throw new NotImplementedException();
}
/othercode
}

42. Supported By:
BENTO
public class CustomerIsPremium extends
AbstractSpecification<Customer> {
private OrderRepository orderRepository
public CustomerIsPremium(OrderRepository orderRepository) {
this.orderRepository = orderRepository;
}
@Override
public boolean isSatisfiedBy(Customer customer) {
int count =
this.orderRepository.countByCustomer(customer.getId);
return (count > 3);
}
}
PRACTICE

43. Supported By:
PRACTICE
BENTO
@Test
public void specification_customer_premium() {
CustomerIsPremium<Customer> spec= new CustomerIsPremium();
customer2order = …
customer3order = …
assertFalse(spec.isSatisfiedBy(customer2order));
assertTrue(spec.isSatisfiedBy(customer3order));
}
TEST PASSED

44. Supported By:
JOKO
PRACTICE
“different rules apply for different
tenants.”

45. Supported By:
BENTO
public class CustomerWith3OrdersIsPremium implement
CustomerIsPremium {}
public class CustomerWith500kPremium implement
CustomerIsPremium {}
public class CustomerWithSpecialRequiredmentPremium
implement CustomerIsPremium {}
PRACTICE
Specification Interface
public interface CustomerIsPremium extends
Specification<Customer> {
boolean isSatisfiedBy(Customer cust);
}

46. Supported By:
BENTO
PRACTICE
public class SpecialOfferSender {
private CustomerIsPremium premiumSpec
public SpecialOfferSende(CustomerIsPremium premiumSpec) {
this.orderRepository = orderRepository;
}
public void sendOffersTo(Customer customer) {
if (this.premiumSpec.isSatisfiedBy(customer)) {
//send offers
}
}
}

47. Supported By:
Use Spefication for Object Selection
REFACTORING

48. Supported By:
JOKO
PRACTICE
“get a list of all premium customers”

49. Supported By:
PRACTICE
 Intro to predicate pattern
 Collection predicate
 JPA predicate

50. Supported By:
BENTO
PRACTICE
Specification Interface
public interface Specification<T> {
boolean isSatisfiedBy(T t);
Predicate toCollectionPredicate();
}
@Override
public Predicate toCollectionPredicate(Customer customer) {
Predicate<Customer> predicate =
new predicate<Customer>() {
@Override
public boolean apply(Customer input) {
return this.isSatisfiedBy(input);
}
};
return predicate;
}

51. Supported By:
BENTO
PRACTICE
CustomerIsPremium<Customer> spec= new CustomerIsPremium();
List<Customer> allCustomer = …
Collection<Customer> result =
Collections2.filter(
allCustomer,
spec.toCollectionPredicate()
);
assertArrayEquals(result, … testarray);
TEST PASSED

52. Supported By:
BENTO
PRACTICE
Specification Interface
public interface Specification<T> {
boolean isSatisfiedBy(T t);
Predicate toCollectionPredicate();
Predicate toPredicate(Root<T> root, CriteriaBuilder cb);
}
@Override
public Predicate toPredicate
(Root<Customer> root, CriteriaBuilder cb) {
return
cb.and (cb.greaterThan(root.get(Customer_.order),3)
);
}

53. Supported By:
BENTO
PRACTICE
public class DBRepository {
private EntityManager entityManager = ...
public <T> List<T> findAllBySpecification(Specification<T> specification) {
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
// use specification.getType() to create a Root<T> instance
CriteriaQuery<T> criteriaQuery = criteriaBuilder.createQuery(specification.getType());
Root<T> root = criteriaQuery.from(specification.getType());
// get predicate from specification
Predicate predicate = specification.toPredicate(root, criteriaBuilder);
// set predicate and execute query
criteriaQuery.where(predicate);
return entityManager.createQuery(criteriaQuery).getResultList();
}
}

54. Supported By:
BENTO
PRACTICE
CustomerIsPremium<Customer> spec= new CustomerIsPremium();
List<Customer> Customer = DBRepository.
findAllBySpecification(spec);
assertArrayEquals(result, … testarray);
TEST PASSED

55. Supported By:
SUMMARY
 Protect your invariants
 Use object as consistency boundaries
 Encapulate state and behavior with value object
 Encapulate Operations
 Use specification pattern
 Use predicate pattern

56. Supported By:
Questions ?

57. Supported By:
Identity CTM for Refactoring,
each monday
REFACTORING

58. Supported By:
Thanks