处理运行时依赖项

正如我所写的,你所谓的“样板代码”在我看来只是“代码”。您需要在某个地方声明一些处理逻辑(本地事件转到本地事件处理器,等等)。试图避免明确说明逻辑可能是错误的。

如果您确实希望这样做,最简单的方法是更改接口以添加方法:

boolean isInterestedInEvent(Event e)

然后设置所有事件处理器,并在其上循环,直到找到正确的事件处理器。

你可以用像这样的东西

public interface EventProcessor {
    public boolean supports(Event event, User user);
    public void handleEvent(Event event);
}

class EventProcessorFactory {
    public void setEventProcessors(List<EventProcessor> processors) {
        this.processors = processors;
    }
    public EventProcessor get(Event event, User user) {
        for (EventProcessor processor : processors) {
            if (processor.supports(event, user)
                return processor;
        }
    }
}

class LocalEventProcessor implements EventProcessor {
   public boolean supports(Event event, User user) {
        return (event instanceof LocalEvent);
   }
   // etc
}

class RemoteEventProcessor implements EventProcessor {
    public boolean supports(Event event, User user) {
        return (event instanceof RemoteTriggeredEvent) &&
               (user instanceof AdminUser);
    }
    // etc
}

Comparable 为了确保它们以正确的顺序进行测试,否则您可以依赖于它们以所需的顺序注入工厂,从而使其可配置。

Event 负责创建 EventProcessor . 这样可以减少 instanceof

public interface Event {
  EventProcessor createProcessor(User u);
}

public class RemoteTriggeredEvent implements Event {
  public EventProcessor createProcessor(User u) {
    return (u instanceof AdminUser) ? new RemoteEventProcessor(u) :
      new DefaultEventProcessor();
  }
}