Observer
定义：观察者模式定义了对象之间的一对多依赖，当一个对象的状态改变时，它的所有依赖者都会收到通知并更新。Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
在具体实现时需要注意：
- 若是循环同步通知，需要注意观察者的执行时间，若执行太久，则会阻塞后面观察者。可以使用异步、超时等方法解决。
- 需要注意重复注册观察者问题。
又叫监听器模式、发布/订阅模式。
注意要先调用 setChanged 方法。
缺点：Observable 是一个类而不是接口，而且本身也没有实现接口。
package com.google.common.eventbus;
public class EventBus {
private final SubscriberRegistry subscribers = new SubscriberRegistry(this);
public void register(Object object) {
subscribers.register(object);
}
public void unregister(Object object) {
subscribers.unregister(object);
}
public void post(Object event) {
Iterator<Subscriber> eventSubscribers = subscribers.getSubscribers(event);
if (eventSubscribers.hasNext()) {
dispatcher.dispatch(event, eventSubscribers);
} else if (!(event instanceof DeadEvent)) {
// the event had no subscribers and was not itself a DeadEvent
post(new DeadEvent(this, event));
}
}
}
final class SubscriberRegistry {
private final ConcurrentMap<Class<?>, CopyOnWriteArraySet<Subscriber>> subscribers =
Maps.newConcurrentMap();
}
Last modified 3yr ago