监听器模式

事件源

持有关注在该消息源上的消息监听器列表，事件发生后通过监听列表进行事件透出。

public class EventSource {
    private List<TimeoutEventListener> timeoutEventListeners;
    public EventSource() {
        timeoutEventListeners = new ArrayList<>();
        timeoutEventListeners.add(new SendAlertTimeoutEventListener());
        timeoutEventListeners.add(new SendFileTimeoutEventListener());
    }
    public static void main(String[] args) {
        new EventSource().doSomething();
    }
    public void doSomething(){
        LocalDateTime expireDate = LocalDateTime.of(2019, 12, 20, 23, 4);
        if (expireDate.isBefore(LocalDateTime.now())){
            System.out.println("触发某个业务的超时事件");
            publishEvent(new TimeoutEventObject(expireDate));
        }
    }
    private void publishEvent(TimeoutEventObject arg){
        for (TimeoutEventListener listener : timeoutEventListeners) {
            listener.onTimeout(arg);
        }
    }
}

监听器

TimeoutEventObject是事件对象，可以定义事件需要透传的属性。 TimeoutEventListener是继承jdk中的EventListener，但这是一个标记接口（无任何规范接口）。 SendAlertTimeoutEventListener和SendFileTimeoutEventListener是业务对监听器的不同实现。

public interface TimeoutEventListener extends EventListener {
    void onTimeout(TimeoutEventObject eventObject);
}
public class SendAlertTimeoutEventListener implements TimeoutEventListener {
    @Override
    public void onTimeout(TimeoutEventObject eventObject) {
        System.out.println("发送过期消息给钉钉,过期时间:"+eventObject.getExpireDate());
    }
}
public class SendFileTimeoutEventListener implements TimeoutEventListener {
    @Override
    public void onTimeout(TimeoutEventObject eventObject) {
        System.out.println("发送过期消息给文件,过期时间:"+eventObject.getExpireDate());
    }
}
public class TimeoutEventObject extends EventObject {
    private LocalDateTime expireDate;
    public LocalDateTime getExpireDate() {
        return expireDate;
    }
    public void setExpireDate(LocalDateTime expireDate) {
        this.expireDate = expireDate;
    }
    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public TimeoutEventObject(Object source) {
        super(source);
        this.expireDate = (LocalDateTime)source;
    }
}