关于ddd:聊聊cheddar的DomainEvent

序

本文次要钻研一下 cheddar 的 DomainEvent

DomainEvent

Cheddar/cheddar/cheddar-domain/src/main/java/com/clicktravel/cheddar/domain/event/DomainEvent.java

public interface DomainEvent extends Event {}

DomainEvent 接口继承了 Event 接口

AbstractDomainEvent

Cheddar/cheddar/cheddar-domain/src/main/java/com/clicktravel/cheddar/domain/event/AbstractDomainEvent.java

public abstract class AbstractDomainEvent extends AbstractEvent implements DomainEvent {public abstract String context();

    @Override
    public final String type() {return context() + "." + getClass().getSimpleName();
    }

}

AbstractDomainEvent 继承了 AbstractEvent，申明实现了 DomainEvent 接口，它申明了一个形象的 context 办法

DomainEventHandler

Cheddar/cheddar/cheddar-domain/src/main/java/com/clicktravel/cheddar/domain/event/DomainEventHandler.java

public interface DomainEventHandler extends EventHandler<DomainEvent> {

}

public interface HighPriorityDomainEventHandler extends DomainEventHandler {

}

public interface LowPriorityDomainEventHandler extends DomainEventHandler {}

DomainEventHandler 接口继承了 EventHandler 接口，其泛型为 DomainEvent；HighPriorityDomainEventHandler 及 LowPriorityDomainEventHandler 接口继承了 DomainEventHandler 接口

DomainEventPublisher

Cheddar/cheddar/cheddar-domain/src/main/java/com/clicktravel/cheddar/domain/event/DomainEventPublisher.java

public class DomainEventPublisher extends EventPublisher<DomainEvent> {

    private static DomainEventPublisher instance;

    public static void init(final MessagePublisher<TypedMessage> messagePublisher) {instance = new DomainEventPublisher(messagePublisher);
    }

    private DomainEventPublisher(final MessagePublisher<TypedMessage> messagePublisher) {super(messagePublisher);
    }

    public static DomainEventPublisher instance() {if (instance == null) {throw new IllegalStateException("DomainEventPublisher not initialized");
        }
        return instance;
    }

}

DomainEventPublisher 继承了 EventPublisher，其结构器接管 MessagePublisher；它提供了 init 办法用于创立 DomainEventPublisher，instance 办法用于获取 instance

小结

cheddar 定义了 DomainEvent 接口及 AbstractDomainEvent 抽象类；DomainEventHandler 接口继承了 EventHandler 接口，其泛型为 DomainEvent；DomainEventPublisher 继承了 EventPublisher，其结构器接管 MessagePublisher，其 publishEvent 办法最初通过 MessagePublisher 的 publish 来实现。

doc

• Cheddar