一、觀察者模式定義
類型：行為型模式
目的：當一個對象的狀態(tài)發(fā)生改變時，其所有依賴者（觀察者）都會收到通知并自動更新。
二、例子
2.1 菜鳥教程例子
2.1.1 定義觀察者
//觀察者
public abstract class Observer {
//被觀察對象
protected Subject subject;
public abstract void update();
}
public class BinaryObserver extends Observer{
public BinaryObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Binary String: " + Integer.toBinaryString( subject.getState() ) );
}
}
public class HexaObserver extends Observer{
public HexaObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Hex String: " + Integer.toHexString( subject.getState() ).toUpperCase() );
}
}
2.1.2 定義被觀察對象
import java.util.ArrayList;
import java.util.List;
//被觀察對象
public class Subject {
//觀察者列表
private List<Observer> observers = new ArrayList<Observer>();
private int state;
public int getState() {
return state;
}
public void attach(Observer observer){
observers.add(observer);
}
//通知所有觀察者
public void notifyAllObservers(){
for (Observer observer : observers) {
observer.update();
}
}
//修改數(shù)據(jù)時，通知所有觀察者
public void setState(int state) {
this.state = state;
notifyAllObservers();
}
}
2.1.3 使用
public class ObserverPatternDemo {
public static void main(String[] args) {
//創(chuàng)建被觀察對象
Subject subject = new Subject();
//創(chuàng)建觀察者對象
new HexaObserver(subject);
new BinaryObserver(subject);
//創(chuàng)建被觀察對象調(diào)用setState時，通知國有觀察者
System.out.println("First state change: 15");
subject.setState(15);
System.out.println("Second state change: 10");
subject.setState(10);
}
}
2.2 JDK源碼 —— Observable
2.2.1 觀察者接口Observer
public interface Observer {
void update(Observable o, Object arg);
}
2.2.1 被觀察者對象Observable
public class Observable {
private boolean changed = false;
private Vector<Observer> obs;
//添加觀察者
public synchronized void addObserver(Observer o) {
if (o == null)
throw new NullPointerException();
if (!obs.contains(o)) {
obs.addElement(o);
}
}
//通知觀察者
public void notifyObservers(Object arg) {
Object[] arrLocal;
synchronized (this) {
if (!changed)
return;
arrLocal = obs.toArray();
clearChanged();
}
for (int i = arrLocal.length-1; i>=0; i--)
((Observer)arrLocal[i]).update(this, arg);
}
}
2.3 Spring源碼 —— AbstractApplicationContext
2.3.1 觀察者
public class ContextStartedEvent extends ApplicationContextEvent {
public ContextStartedEvent(ApplicationContext source) {
super(source);
}
}
public class ContextStoppedEvent extends ApplicationContextEvent {
public ContextStoppedEvent(ApplicationContext source) {
super(source);
}
}
public class ContextRefreshedEvent extends ApplicationContextEvent {
public ContextRefreshedEvent(ApplicationContext source) {
super(source);
}
}
2.3.2 被觀察者
public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext {
//觀察者集合
private Set<ApplicationEvent> earlyApplicationEvents;
//添加觀察者Event
public void publishEvent(ApplicationEvent event) {
this.publishEvent(event, (ResolvableType)null);
}
//通知觀察者Event
protected void registerListeners() {
Iterator var1 = this.getApplicationListeners().iterator();
while(var1.hasNext()) {
ApplicationListener<?> listener = (ApplicationListener)var1.next();
this.getApplicationEventMulticaster().addApplicationListener(listener);
}
String[] listenerBeanNames = this.getBeanNamesForType(ApplicationListener.class, true, false);
String[] var7 = listenerBeanNames;
int var3 = listenerBeanNames.length;
for(int var4 = 0; var4 < var3; ++var4) {
String listenerBeanName = var7[var4];
this.getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}
Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
this.earlyApplicationEvents = null;
if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
Iterator var9 = earlyEventsToProcess.iterator();
while(var9.hasNext()) {
ApplicationEvent earlyEvent = (ApplicationEvent)var9.next();
this.getApplicationEventMulticaster().multicastEvent(earlyEvent);
}
}
}
}
2.3 Guava源碼 —— EventBus
public class EventBus {
//注冊訂閱者（觀察者）
public void register(Object object) {
this.subscribers.register(object);
}
//通知訂閱者（觀察者）
public void post(Object event) {
Iterator<Subscriber> eventSubscribers = this.subscribers.getSubscribers(event);
if (eventSubscribers.hasNext()) {
this.dispatcher.dispatch(event, eventSubscribers);
} else if (!(event instanceof DeadEvent)) {
this.post(new DeadEvent(this, event));
}
}
}
三、其他設(shè)計模式
創(chuàng)建型模式
結(jié)構(gòu)型模式文章來源：http://www.zghlxwxcb.cn/news/detail-735521.html
- 1、設(shè)計模式——裝飾器模式（Decorator Pattern）+ Spring相關(guān)源碼
行為型模式文章來源地址http://www.zghlxwxcb.cn/news/detail-735521.html
- 1、設(shè)計模式——訪問者模式（Visitor Pattern）+ Spring相關(guān)源碼
- 2、設(shè)計模式——中介者模式（Mediator Pattern）+ JDK相關(guān)源碼
- 3、設(shè)計模式——策略模式（Strategy Pattern）+ Spring相關(guān)源碼
- 4、設(shè)計模式——狀態(tài)模式（State Pattern）
- 5、設(shè)計模式——命令模式（Command Pattern）+ Spring相關(guān)源碼
- 6、設(shè)計模式——觀察者模式（Observer Pattern）+ Spring相關(guān)源碼
- 7、設(shè)計模式——備忘錄模式（Memento Pattern）
- 8、設(shè)計模式——模板方法模式（Template Pattern）+ Spring相關(guān)源碼
- 9、設(shè)計模式——迭代器模式（Iterator Pattern）+ Spring相關(guān)源碼
- 10、設(shè)計模式——責(zé)任鏈模式（Chain of Responsibility Pattern）+ Spring相關(guān)源碼
- 11、設(shè)計模式——解釋器模式（Interpreter Pattern）+ Spring相關(guān)源碼
到了這里，關(guān)于設(shè)計模式——觀察者模式（Observer Pattern）+ Spring相關(guān)源碼的文章就介紹完了。如果您還想了解更多內(nèi)容，請在右上角搜索TOY模板網(wǎng)以前的文章或繼續(xù)瀏覽下面的相關(guān)文章，希望大家以后多多支持TOY模板網(wǎng)！
