聊聊cheddar的events

时间 2021-03-26

标签 java git github json app ide this debug code 接口栏目 Java 繁體版

原文原文链接

序

本文主要研究一下cheddar的eventsjava

Event

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

public interface Event {

    String type();

    String serialize();

}

Event接口定义了type、serialize方法

AbstractEvent

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

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声明实现Event接口，它实现了serialize方法，采用jackson序列化为json；而后声明type抽象方法供子类实现

EventHandler

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

public interface EventHandler<E extends Event> {

    void handle(final E event);

    Class<? extends E> getEventClass();

}

EventHandler接口定义了handle、getEventClass方法

EventPublisher

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

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方法定义了publishEvent方法，它建立SimpleMessage，而后执行messagePublisher的publish来发布消息

小结

cheddar定义了Event接口及AbstractEvent抽象类，其子类须要实现type方法；EventHandler接口定义了handle、getEventClass方法；EventPublisher方法定义了publishEvent方法，它建立SimpleMessage，而后执行messagePublisher的publish来发布消息。ide

doc

Cheddar