adam bien's blog

The classic DTO solves the following problem:

"You want to transfer multiple data elements over a tier."

Back in the days a DTO was implemented as a Serializable anemic Java class only equipped with field accessors.

In Java EE the https://jax-rs-spec.java.net became a de-facto standard for remoting, so the implementation of Serializable interface is no more required. To transfer data between tiers in Java EE 7 you get the following options for free:

1. JAXB: the popular application servers offer JSON, XML serialization for "free".

   
   @Entity
   @XmlRootElement
   @XmlAccessorType(XmlAccessType.FIELD)
   @NamedQuery(name = Registration.findAll, query = "SELECT r FROM Registration r")
   public class Registration {
   
       private static final String PREFIX = "com.airhacks.workshops.business.registrations.entity.Registration.";
       public static final String findAll = PREFIX + "all";
   
   
       @Id
       @GeneratedValue
       @XmlTransient
       private long id;
   
       @XmlTransient
       @Transient
       private BiFunction<Boolean, Integer, Integer> taxCalculator;
   
       private int numberOfDays;
       private int numberOfAttendees;
       private boolean vatIdAvailable;
       
       //...
   
   }
   
   

   [Registration.java from https://github.com/AdamBien/javaee-bce-archetype]
2. With the introduction of Java API for JSON Processing, you can also directly serialize parts of your objects into JSON:

   
   @Path("health")
   @Produces(MediaType.APPLICATION_JSON)
   public class HealthResource {
   
       @Inject
       ServerWatch watch;
   
   
       @GET
       @Path("/current-memory")
       public JsonObject availableHeap() {
    JsonObjectBuilder builder = Json.createObjectBuilder();
   	builder.add("Available memory in mb", this.watch.availableMemoryInMB()).
   	add("Used memory in mb", this.watch.usedMemoryInMb());
   	return builder.build();
       }
       
       //...
   }
   
   

   [HealthResource.java from project ping]

Both approaches transport the data without any binary coupling to the origin object. The decoupling is even higher, as it was the case with the "traditional" (=code duplication) DTO implementation.

[See also an in-depth discussion in the "Real World Java EE Night Hacks--Dissecting the Business Tier" book, page 273 in, chapter "Data Transfer Object"]

See you at Java EE Workshops at MUC Airport or on demand and in a location very near you: airhacks.io!