1. @joachimvda@eliwan_be
converting between transfer and domain
objects
Joachim Van der Auwera

2. @joachimvda@eliwan_be
What is a tranfer object
• Class with only getters and
setters
• Project Lombok recommended @Data
Public class PersonTo {
private String firstName;
private String lastName;
private String gender;
private String birthday;
}

3. @joachimvda@eliwan_be
Why use transfer objects
• Decouple API and domain
model
• Manage application boundaries
(e.g. transactions)
@Data
@Entity
Public class Person {
@Id
Private Long id;
@Basic
private String firstName;
@Basic
private String lastName;
@Basic
private Gender gender;
@Basic
private LocalDate birthday;
}

4. @joachimvda@eliwan_be
How?
• Stupid boilerplate conversion
code
Public Person toDomain(
PersonTo to) {
Person res = new Person();
Res.setFirstName(
to.getFirstName());
...
Return res;
}

5. @joachimvda@eliwan_be
Not always simple...
• Null checks
• Domain lookup
• Type conversion
• Still boilerplate !
Gender gender;
if (StringUtils.
isBlank(to.getGender)) {
Gender = null;
} else {
Gender = Gender.valueOf(
to.getGender());
}
res.setGender(gender);

6. @joachimvda@eliwan_be
In the real world...
• Project for Flemish Government, REST API
• almost 10% of the code was custom conversion between TO and domain
objects
• Inconsistent conversion behaviour
• Stupid work, easy to make mistakes
• Testing

7. @joachimvda@eliwan_be
Automate
• Automatic conversion...
• jTransfo
• dozer

8. @joachimvda@eliwan_be
jTransfo features
• Easy to use
• Annotation based
• No dependencies
• Many transfer objects – one domain object
• Security enabled

9. @joachimvda@eliwan_be
Integrations
• Spring framework
• CDI
• Joda-time
• Hibernate
• JRebel
• Works well with Project Lombok (highly recommended!)

10. @joachimvda@eliwan_be
Easy conversion
JTransfo jTransfo = new JTransfoImpl();
SomeDomain domainObject = jTransfo.
convertTo(transferObject, SomeDomain.class);
SomeDomain domainObject = new SomeDomain();
jTransfo.convert(transferObject, domainObject);
List<SomeDomain> list = jTransfo.
convertList(transferObjects, SomeDomain.class);

11. @joachimvda@eliwan_be
Easy conversion
@Data
@DomainClass("pkg.Person")
public class PersonTo {
private String name;
@MappedBy(field = “country”, path = “addr”)
private String addrCountry;
@MappedBy(readOnly = true)
private String gender;
@NotMapped
private String globaalNummer;
}

12. @joachimvda@eliwan_be
@MapOnlies({
@MapOnly("create"),
@MapOnly(value = "*", readOnly = true)
})
private String somefield;
Security
jTransfo.convertTo(transferObject,
SomeDomainClass.class, “create”, “admin”);

13. @joachimvda@eliwan_be
Type conversion and lists
@MappedBy(typeConverter = "filterToList")
private List<FilterTo> filters;
@MappedBy(typeConverter = "readOnlyDomain")
private LayerTo layer;

14. @joachimvda@eliwan_be
Type conversion, Spring config
<import resource=
"classpath:org/jtransfo/spring/jTransfoContext.xml" />
<bean
class="org.jtransfo.ReadOnlyDomainTypeConverter" />
<bean class="org.jtransfo.ReadOnlyDomainListTypeConverter">
<constructor­arg value="filterToList" />
<constructor­arg value="pkg.FilterTo" />
<property name="sortList" value="true" />
</bean>

15. @joachimvda@eliwan_be
ORM link, object finder
Automatically build new / linked object
•Find in Hibernate maybe
•Always consistent
Use ReadOnlyDomain to either update links only or linked object contents as well

16. @joachimvda@eliwan_be
Inheritance support
Declare child types to convert to correct object
Normal annotations on child classes (correct domain class)
@DomainClass(value = "pkg.ObjectDomain")
@DomainClassDelegate(delegates = {
SomeChildTo.class, OtherChildTo.class
})
public class ObjectTo {

17. @joachimvda@eliwan_be
Convert interceptor
Set method to call on each convert invocation
Validations
Side effects
<T> T convert(
Object source,
T target,
boolean isTargetTo,
ConvertSourceTarget next,
String... tags);

18. @joachimvda@eliwan_be
www.jtransfo.org
https://github.com/joachimvda/jtransfo