聊聊cheddar的events

序

本文主要研究一下cheddar的events

Event

Cheddar/cheddar/cheddar-events/src/main/java/com/clicktravel/cheddar/event/Event.java

public interface Event {

    String type();

    String serialize();

}

Event接口定義了type、serialize方法

AbstractEvent

Cheddar/cheddar/cheddar-events/src/main/java/com/clicktravel/cheddar/event/AbstractEvent.java

public abstract class AbstractEvent implements Event {

    private static final ObjectMapper MAPPER = new ObjectMapper();

    static {
        MAPPER.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        MAPPER.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        MAPPER.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        MAPPER.registerModule(new JodaModule());
    }

    @Override
    public abstract String type();

    public static <T extends Event> T newEvent(final Class<T> eventClass, final String serializedEvent) {
        try {
            return MAPPER.readValue(serializedEvent, eventClass);
        } catch (final IOException e) {
            throw new IllegalStateException("Could not instantiate event " + eventClass.getName());
        }
    }

    @Override
    public final String serialize() {
        try {
            return MAPPER.writeValueAsString(this);
        } catch (final Exception e) {
            throw new IllegalStateException("Could not serialize event: [" + this + "]", e);
        }
    }

}

AbstractEvent聲明實現Event接口，它實現了serialize方法，採用jackson序列化爲json；而後聲明type抽象方法供子類實現

EventHandler

Cheddar/cheddar/cheddar-events/src/main/java/com/clicktravel/cheddar/event/EventHandler.java

public interface EventHandler<E extends Event> {

    void handle(final E event);

    Class<? extends E> getEventClass();

}

EventHandler接口定義了handle、getEventClass方法

EventPublisher

Cheddar/cheddar/cheddar-events/src/main/java/com/clicktravel/cheddar/event/EventPublisher.java

public abstract class EventPublisher<E extends Event> {

    private final Logger logger = LoggerFactory.getLogger(getClass());
    private final MessagePublisher<TypedMessage> messagePublisher;

    protected EventPublisher(final MessagePublisher<TypedMessage> messagePublisher) {
        this.messagePublisher = messagePublisher;
    }

    public void publishEvent(final E event) {
        logger.debug("Publishing: " + event);
        final TypedMessage typedMessage = new SimpleMessage(event.type(), event.serialize());
        messagePublisher.publish(typedMessage);
    }

}

EventPublisher方法定義了publishEvent方法，它建立SimpleMessage，而後執行messagePublisher的publish來發布消息

小結

cheddar定義了Event接口及AbstractEvent抽象類，其子類須要實現type方法；EventHandler接口定義了handle、getEventClass方法；EventPublisher方法定義了publishEvent方法，它建立SimpleMessage，而後執行messagePublisher的publish來發布消息。

doc

• Cheddar