监听器模式
监听器模式其实是观察者模式中的一种，两者都有关于回调的设计。
与观察者模式不同的是，观察者模式中存在的角色为观察者(Observer)和被观察者(Observable)
而监听器模式中存在三种角色
- 事件源(EventSource)
- 事件对象(EventObject)
- 事件监听器(EventListener)
简单的概述就是: 事件源经过事件的封装传给监听器，当事件源触发事件后，监听器接收到事件对象可以回调事件的方法
下面这张图可以很详细解释他们之间的关系
简单的实例
UML
@startuml
class EventSource{
- listeners: Vector<EventListener>
+ void addListener(EventListener listener)
+ void removeListener(EventListener listener)
+ void notifyListenerEvents(EventObject eventObject)
}
class EventObject{
+ getSource(): Object
+ void:say()
}
interface EventListener{
+ void handleEvent(EventObject eventObject)
}
class ConcreteEvetListenerA{
+ void handleEvent(EventObject eventObject)
}
class ConcreteEvetListenerB{
+ void handleEvent(EventObject eventObject)
}
EventListener <-- ConcreteEvetListenerA
EventListener <-- ConcreteEvetListenerB
EventObject --o EventListener
EventSource -- EventObject
@enduml
事件源
public class DemoEventSource {
/** 监听器列表 */
public Vector<DemoEventListener> listeners = new Vector<>();
/**
* 注册监听器
* @param listener EventListener
*/
public void addListener(DemoEventListener listener) {
listeners.add(listener);
}
/**
* 撤销监听器
* @param listener EventListener
*/
public void removeListener(DemoEventListener listener) {
listeners.remove(listener);
}
/**
* 通知所有监听器,包裹事件源成为事件
* @param eventObject EventObject
*/
public void notifyListenerEvents(EventObject eventObject){
listeners.forEach(listener ->{
listener.handleEvent(eventObject);
});
}
}
事件对象
public class DemoEventObject extends EventObject {
/**
* Constructs a prototypical Event.
*
* @param source The object on which the Event initially occurred.
* @throws IllegalArgumentException if source is null.
*/
public DemoEventObject(Object source) {
super(source);
}
/**
* 事件的回调或者业务逻辑
*/
public void say() {
System.out.println("this is " + this + " to say");
}
}
事件监听器
public interface DemoEventListener extends EventListener {
/**
* 处理事件
* @param eventObject EventObject
*/
void handleEvent(EventObject eventObject);
}
public class ConcreteEventListenerA implements DemoEventListener {
@Override
public void handleEvent(EventObject eventObject) {
System.out.println("ConcreteEventListenerA accept eventObject , eventSource is : " + eventObject.getSource());
if (eventObject instanceof DemoEventObject) {
// 执行事件的回调函数/具体业务逻辑
((DemoEventObject) eventObject).say();
}
}
}
public class ConcreteEventListenerB implements DemoEventListener {
@Override
public void handleEvent(EventObject eventObject) {
System.out.println("ConcreteEventListenerB accept eventObject , eventSource is : " + eventObject.getSource());
if (eventObject instanceof DemoEventObject) {
// 执行事件的回调函数/具体业务逻辑
((DemoEventObject) eventObject).say();
}
}
}
客户端
public class Client {
public static void main(String[] args) {
// 初始化监听器
DemoEventListener demoEventListenerA = new ConcreteEventListenerA();
DemoEventListener demoEventListenerB = new ConcreteEventListenerB();
// 事件源A
DemoEventSource demoEventSource1 = new DemoEventSource();
demoEventSource1.addListener(demoEventListenerA);
demoEventSource1.addListener(demoEventListenerB);
demoEventSource1.notifyListenerEvents(new DemoEventObject(demoEventSource1));
// 事件源B
DemoEventSource demoEventSource2 = new DemoEventSource();
demoEventSource2.addListener(demoEventListenerB);
demoEventSource2.notifyListenerEvents(new DemoEventObject(demoEventSource2));
}
}