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© GameDuell GmbH | DOAG 2015

Cargo Tracker

Domain-Driven Design auf Basis von JEE

Dirk Ehms, GameDuell GmbH


Domain-Driven Design

• Set of principles and patterns

• Not a technology or methodology

• Software and domain experts collaboration

• Term invented by Eric Evans

2


Java Pet Store / J2EE Core Pattern

3


Cargo Tracker

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Cargo Tracker Screenshot

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Domain-Driven Design Reference Definitions and Pattern Summaries

6

http://tinyurl.com/k82tpbr

https://domainlanguage.com/ddd/patterns/DDD_Reference_2011-01-31.pdf


Building Blocks of DDD: Model-Driven Design

Value Objects

Repositories

Services

Model-Driven Design

Layered Architecture

Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of

Maintain integrity with

Domain Events

Express model with Push state change with


Cargo Tracker Domain Model

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Building Blocks of DDD: Layered Architecture

Value Objects

Repositories

Services

Model-Driven Design

Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events





10 Source: [Evans, DDD]


Building Blocks of DDD: Entities

Value Objects

Repositories

Services

Model-Driven Design


Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events



Entities

• Have identity, state and behavior

• Not defined by their attributes

• Examples: Customer, Account

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@Entity public class Cargo implements Serializable { private TrackingId trackingId; public void specifyNewRoute(RouteSpecification routeSpecification) {...} public void assignToRoute(Itinerary itinerary) {...} public void deriveDeliveryProgress(HandlingHistory handlingHistory) {...} ... }


Domain Model: Entities

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Building Blocks of DDD: Value Objects

Value Objects

Repositories

Services

Model-Driven Design


Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events



Value Objects

• Defined by their attributes

• No conceptual identity

• Immutable

• Entity contains Value Objects

• Examples: Address, Money

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@Embeddable public class Itinerary implements Serializable { /** * Test if the given handling event is expected when executing this * itinerary. */ public boolean isExpected(HandlingEvent event) {...} ... }


Value Objects (cont.)

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@Embeddable public class Itinerary implements Serializable { @OrderBy("loadTime") @PrivateOwned @Size(min = 1) private List<Leg> legs = Collections.emptyList(); ... }

@Entity public class Leg implements Serializable { @Id @GeneratedValue private Long id; ... }


Building Blocks of DDD: Aggregates

Value Objects

Repositories

Services

Model-Driven Design


Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events



Aggregates

• Cluster of Entities and Value Objects

• Consistency boundary

• One Entity acts as Aggregate Root

• Root controls access

• Root is target for external references

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Aggregates (cont.)

@Entity

public class Cargo implements Serializable {

@Id

@GeneratedValue

private Long id;

@Embedded

private TrackingId trackingId;

@ManyToOne

@JoinColumn(name = "origin_id")

private Location origin;

@Embedded

private RouteSpecification routeSpecification;

@Embedded

private Itinerary itinerary;

@Embedded

private Delivery delivery;

public void specifyNewRoute(RouteSpecification routeSpecification) {...}

public void assignToRoute(Itinerary itinerary) {...}

public void deriveDeliveryProgress(HandlingHistory handlingHistory) {...}

...

}


Domain Model: Aggregates

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Alternative Approaches

• ID references between aggregates

• Custom Types

• ORM file instead of annotations

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<?xml version="1.0" encoding="UTF-8"?> <entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm http://java.sun.com/xml/ns/persistence/orm_2_0.xsd" version="2.0"> <entity class="...domain.model.cargo.Cargo" access="FIELD"> ... </entity> <embeddable class="...domain.model.cargo.Itinerary" access="FIELD"> ... </embeddable> </entity-mappings>


Building Blocks of DDD: Repositories

Value Objects

Repositories

Services

Model-Driven Design


Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events



Repositories

• Encapsulates persistence and retrieval

• Interface definition: Domain layer

• Implementation: Infrastructure layer

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@ApplicationScoped public class JpaCargoRepository implements CargoRepository, Serializable { @PersistenceContext private EntityManager entityManager; @Override public Cargo find(TrackingId trackingId) {...} @Override public void store(Cargo cargo) {...} @Override public TrackingId nextTrackingId() {...} ... }


Alternative: Hexagonale Architecture

User Interface Layer Infrastructure Layer

Domain Layer

Internal UI port

External integration

port

In -Memory Database

Relational Database

External systems

NoSQL Database

User Interface

Test adapter

Test adapter

RESTful webservices

Internal persistence

port

External service

port


Building Blocks of DDD: Factories

Value Objects

Repositories

Services

Model-Driven Design


Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events



Factories

• Create complex domain objects

• Relevant Patterns: Factory, Builder

• Invariants

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@ApplicationScoped public class HandlingEventFactory implements Serializable { @Inject private CargoRepository cargoRepository; @Inject private VoyageRepository voyageRepository; @Inject private LocationRepository locationRepository; public HandlingEvent createHandlingEvent(...) {...} ... }


Building Blocks of DDD: Services

Value Objects

Repositories

Services

Model-Driven Design

Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events




Services

• Represent an operation

• Stateless

• Example: transfer(Account1, Account2, Money)

• Domain Service

• Business Logic

• Application Service:

• Non functional requirements, coordinator

• Infrastructure Service

• E.g. sending emails

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Application Service

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@Stateless public class DefaultBookingService implements BookingService { @Inject private CargoRepository cargoRepository; @Inject private LocationRepository locationRepository; @Inject private RoutingService routingService; @Override public TrackingId bookNewCargo(UnLocode originUnLocode, UnLocode destinationUnLocode, Date arrivalDeadline) {...} @Override public List<Itinerary> requestPossibleRoutesForCargo(TrackingId trackingId) {...} @Override public void assignCargoToRoute(Itinerary itinerary, TrackingId trackingId) {...} @Override public void changeDestination(TrackingId trackingId, UnLocode unLocode) {...} }


Building Blocks of DDD: Domain Events

Value Objects

Repositories

Services

Model-Driven Design

Factories

Entities Aggregates

Access with

Encapsulate with

Act as root of


Domain Events




Domain Events

• Represents a state change

• Plain data

• Immutable

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/** * A HandlingEvent is used to register the event when, * for instance, a cargo is unloaded from a carrier at * a some location at a given time. */ @Entity public class HandlingEvent implements Serializable {...}


Technology Mapping

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Layer Building Block APIs Annotations

User Interface JAX-RS JAX-WS JSF Websocket JEE-Batch

@Path @WebService @Named @ServerEndpoint META-INF/batch-jobs/*.xml

Application Layer Application Service EJB @Stateless

Domain Layer

Entity, Aggregate Value Object Domain Service Domain Event

JPA JPA CDI CDI, JMS

@Entity @Embeddable, @Entity @ApplicationScoped @Inject Event<...>

Infrastructure Layer

Repository (Impl.) Infrastructure Service

JPA, CDI JAX-RS-Client, JAX-WS-Client, JMS, JavaMail

@PersistenceContext


DDD Implementation Effort

33 Source: [Fowler, PoEAA]

Complexity of Domain Logic

Data or Transaction centric

Domain Model

Effo

rt t

o E

nh

ance


Resources, Useful Links

• Cargo Tracker

http://cargotracker.java.net

• Getting Started with Domain-Driven Design

http://refcardz.dzone.com/refcardz/getting-started-domain-driven

• Domain-Driven Design Quickly

http://www.infoq.com/minibooks/domain-driven-design-quickly

• Domain-Driven Design Reference


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http://cargotracker.java.net/






















Books

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Any Questions?

Thank You!

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