事件聚合器模式
public class EventAggregator { /** * 事件聚合器模式: * A system with lots of objects can lead to complexities * when a client wants to subscribe to events. * The client has to find and register for each object individually,* if each object has multiple events then each event requires a separate subscription. * An Event Aggregator acts as a single source of events for many objects. * It registers for all the events of the many objects allowing clients to register with just the aggregator. * 当客户端想要订阅事件时,一个有大量对象的系统会导致复杂性。 * 客户端需要单独查找每个对象并进行注册。 * 如果每个对象都有多个事件,那么每个事件都需要单独的订阅。 * 事件聚合器充当许多对象的单个事件源, * 事件聚合器将注册到所有的事件生成器中,客户端只需要注册到事件聚合器中即可获得通知。 */ @Test public void all() { final KingJoffrey kingJoffrey = new KingJoffrey(); final KingsHand kingsHand = new KingsHand(kingJoffrey); final List<BaseEventEmitter> emitters = Lists.newArrayList(); // 将事件聚合器注册到事件生成器中 emitters.add(new LordBaelish(kingsHand)); emitters.add(new Lordvarys(kingsHand)); emitters.add(new Scout(kingsHand)); Stream.of(Weekday.values()).forEach(day -> emitters.forEach(emitter -> emitter.timePasses(day))); } } /** * 1)具体的事件类型 */ @AllArgsConstructor @Getter enum Event { STARK_SIGHTED("Stark sighted"),WARSHIPS_APPROACHING("Warships approaching"),TRAITOR_DETECTED("Traitor detected"); private String description; } /** * 2)事件监听器 */ interface EventListener { void onEvent(Event event); } /** * 3)事件发射器接口 */ interface EventEmitter { void registerObserver(EventListener eventListener); void notifyObservers(Event event); } @AllArgsConstructor @Getter enum Weekday { MONDAY("Monday"),TUESDAY("Tuesday"),WednESDAY("Wednesday"),THURSDAY("Thursday"),FRIDAY("Friday"),SATURDAY( "Saturday"),SUNDAY("Sunday"); private String description; } /** * 4)事件发射器抽象 */ abstract class BaseEventEmitter implements EventEmitter { // 持有多个事件监听器 private final List<EventListener> eventListeners; public BaseEventEmitter() { eventListeners = Lists.newArrayList(); } @Override public void registerObserver(EventListener eventListener) { eventListeners.add(eventListener); } @Override public void notifyObservers(Event event) { eventListeners.forEach(listener -> listener.onEvent(event)); } public abstract void timePasses(Weekday day); } /** * 5)单纯的事件监听器 */ @Slf4j class KingJoffrey implements EventListener { @Override public void onEvent(Event e) { log.info("Received event from the King‘s Hand: {}",e.toString()); } } /** * 6)组合事件监听器和事件发射器 */ class KingsHand extends BaseEventEmitter implements EventListener { public KingsHand(EventListener eventListener) { registerObserver(eventListener); } @Override public void onEvent(Event event) { notifyObservers(event); } @Override public void timePasses(Weekday day) { // nop } } class LordBaelish extends BaseEventEmitter { public LordBaelish(EventListener eventListener) { registerObserver(eventListener); } @Override public void timePasses(Weekday day) { if (day.equals(Weekday.FRIDAY)) { notifyObservers(Event.STARK_SIGHTED); } } } class Lordvarys extends BaseEventEmitter { public Lordvarys(EventListener eventListener) { registerObserver(eventListener); } @Override public void timePasses(Weekday day) { if (day.equals(Weekday.SATURDAY)) { notifyObservers(Event.TRAITOR_DETECTED); } } } class Scout extends BaseEventEmitter { public Scout(EventListener eventListener) { registerObserver(eventListener); } @Override public void timePasses(Weekday day) { if (day.equals(Weekday.TUESDAY)) { notifyObservers(Event.WARSHIPS_APPROACHING); } } }
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