DDD Base

Domain Driven Design base package for Java.

How to use it in Java?

Please refer https://jitpack.io/#linux-china/ddd-base/1.1.1

Features

• Annotations
• Base classes for entity, domain event etc
• Domain event: follow CloudEvents specification and CloudEvent convert support
• DDD Reactive: https://www.reactive-streams.org/

Components

• Data: Entity, VO and Aggregate
• Behaviour: Repository, Service, Factory and Specification
• Event: Follow CloudEvents spec
• Infrastructure
• CQRS interfaces for command & query

Reactive

DDD + Reactive(RSocket) to make context map easy.

Code Structure

Please visit src/test/java for code structure

If you use Kotlin to develop application, the structure will be different, please add entity, vo and repository in the same kt file.

Events

Please extend DomainEvent or DomainEventBuilder, then use ApplicationEventPublisher to publish the event. please refer https://spring.io/blog/2015/02/11/better-application-events-in-spring-framework-4-2

Attention: Spring framework 5.2 will add reactive support: spring-projects/spring-framework#21831

Event extensions(JavaScript Object):

• Distributed Tracing extension(traceparent, tracestate): embeds context from Distributed Tracing so that distributed systems can include traces that span an event-driven system.
• Dataref(dataref): reference another location where this information is stored
• Partitioning(partitionkey): This extension defines an attribute for use by message brokers and their clients that support partitioning of events, typically for the purpose of scaling.
• Sequence(sequence): describe the position of an event in the ordered sequence of events produced by a unique event source
• Sampling(sampledrate): Sampling
• Multi-tenant(tenantId): Multi-tenant system support

CloudEvents JSONSchema: https://github.com/cloudevents/spec/blob/v0.3/spec.json

How to create event class

• Extend CloudEvent class:

public class LoginEvent extends CloudEvent<String> {

    public LoginEvent(String email, String ip) {
        setData(email);
        setContentType("text/plain");
        setExtension("ip", ip);
    }
}

• Create an event directly

CloudEvent<String> loginEvent = new CloudEvent<String>("text/plain", "[email protected]");

• Event Builder or reactive processor

CloudEvent<String> loginEvent = CloudEventBuilder.<String>newInstance().contentType("text/plain").data("[email protected]").build();

• Non-blocking Event Listener: spring-projects/spring-framework#21831

@Component
public class MyListener {

    @EventListener
    public Mono<Void> handleContextRefresh(ContextRefreshedEvent event) {
        //...
    }

    @EventListener
    public Flux<MyBusinessResponseEvent> handleBusinessEvent(MyBusinessEvent event) {
        //...
    }

    @EventListener
    public CompletableFuture<Void> handleBusinessEvent(MyOtherBusinessEvent event) {
        //...
    }
}

ObjectMapper

• ObjectMapper creation

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

• write as String

objectMapper.writeValueAsString(loginEvent);

• read from json text

objectMapper.readValue(jsonText, new TypeReference<CloudEvent<String>>() {});

References

• CloudEvents Specification: https://github.com/cloudevents/spec/blob/master/spec.md
• Reactive Streams: http://www.reactive-streams.org/
• DDD Reference: https://domainlanguage.com/wp-content/uploads/2016/05/DDD_Reference_2015-03.pdf
• ddd-4-java: Base classes for Domain Driven Design with Java https://github.com/fuinorg/ddd-4-java
• jMolecules – Architectural abstractions for Java with DDD concepts https://github.com/xmolecules/jmolecules
• Domain-Driven Design Crew: https://github.com/ddd-crew
• What is Event Sourcing? https://www.eventstore.com/blog/what-is-event-sourcing
• Event Sourcing and CQRS: https://www.eventstore.com/blog/event-sourcing-and-cqrs
• CQRS Document: https://cqrs.files.wordpress.com/2010/11/cqrs_documents.pdf
• remesh: a DDD framework for large and complex TypeScript/JavaScript applications - https://github.com/remesh-js/remesh