观察者模式定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。这个主题对象在状态上发生变化时，会通知所有观察者对象，让他们能够自动更新自己。今天我们通过模拟按钮的处理事件来深入Java观察者模式的学习。
目录导航
- Java观察者的简要说明
- Java的按钮点击案例
- 使用Java中的Observer来模拟按钮监听事件机制
- Java中的Observer原理的说明
- 使用自定义的Observer来过滤按钮监听事件
- 友情链接
Java观察者的简要说明
观察者模式所涉及的角色有：
● 抽象主题(Subject)角色：抽象主题角色把所有对观察者对象的引用保存在一个聚集（比如ArrayList对象）里，每个主题都可以有任何数量的观察者。抽象主题提供一个接口，可以增加和删除观察者对象，抽象主题角色又叫做抽象被观察者(Observable)角色。
● 具体主题(ConcreteSubject)角色：将有关状态存入具体观察者对象；在具体主题的内部状态改变时，给所有登记过的观察者发出通知。具体主题角色又叫做具体被观察者(Concrete Observable)角色。
● 抽象观察者(Observer)角色：为所有的具体观察者定义一个接口，在得到主题的通知时更新自己，这个接口叫做更新接口。
● 具体观察者(ConcreteObserver)角色：存储与主题的状态自恰的状态。具体观察者角色实现抽象观察者角色所要求的更新接口，以便使本身的状态与主题的状态 像协调。如果需要，具体观察者角色可以保持一个指向具体主题对象的引用。
Java的按钮点击案例
我们建立一个项目去开始今天的测试。项目结构如下：
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" alt="" />
demo很简单，点击button按钮，修改button上显示的文字
package com.huhx.frame; import java.awt.event.ActionEvent;
import java.awt.event.ActionListener; import javax.swing.JButton;
import javax.swing.JFrame; /**
* writer: huhx
*/
public class Jframe extends JFrame {
private JButton button; public Jframe() {
button = new JButton("text");
add(button);
setVisible(true);
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
button.setText("world");
}
});
} public static void main(String[] args) {
new Jframe();
}
}
使用Java中的Observer来模拟按钮监听事件机制
java中的内置观察者模式有两个类：一个是observable被观察者类，一个是observer观察者接口。大体上与自定义模式相同，我们编写程序时只需继承obervable类，具体实现observer接口就可以了。值得注意的是：调用notifyObservers()方法之前，必须先调用setChanged()方法。这是因为observable类中把 changed变量初始化为false,notifyObservers()方法会先检查该变量是否为true,如果不为ture，就不会调用 update()方法，这就要我们调用notifyObservers()之前，先用setChanged()方法将changed变量设置为true。
现在我们以上述例子为引子，使用Java中内置的Observer自己来模拟一个按钮监听事件的案例：
一、 创建一个继承obervable类的被观察者，在案例中也就是Button，类记为：MyButton
package com.huhx.observer; import java.util.Observable;
import java.util.Observer; /**
* @author huhx
*/
public class MyButton extends Observable {
public void addListeners(Observer observer) {
addObserver(observer);
} public void process(Object args) {
setChanged();
notifyObservers(args);
} public void process() {
process(null);
}
}
二、 创建几个观察这个按钮的观察者，其实就是按钮的监听事件：
模拟点击事件：
package com.huhx.observer; import java.util.Observable;
import java.util.Observer; public class ClickObserver implements Observer { @Override
public void update(Observable o, Object arg) {
if (arg != null) {
System.out.println("click: " + arg.toString());
} else {
System.out.println("click no arg");
}
}
}
模拟按下事件：
package com.huhx.observer; import java.util.Observable;
import java.util.Observer; public class PressObserver implements Observer { @Override
public void update(Observable o, Object arg) {
if (arg != null) {
System.out.println("press: " + arg.toString());
} else {
System.out.println("press no arg");
}
}
}
三、 然后我们写一个测试的类，用于模拟按钮的事件：这里的process方法模拟真实按钮的触发事件，通知所有的观察者。比如我们按下按钮。
package com.huhx.observer; import java.util.Observable;
import java.util.Observer; public class PersonTest { public static void main(String[] args) {
MyButton button = new MyButton();
button.addObserver(new ClickObserver()); button.addListeners(new Observer() {
@Override
public void update(Observable o, Object arg) {
System.out.println("observer");
}
});
button.process("huhx");
}
}
五、 它的输出结果如下：
observer
click: huhx
Java中的Observer原理的说明
上述我们通过案例，来模拟了按钮的监听事件原理，现在我们通过源码来详细的分析它的运行过程：
一、 Observer是一个观察者可以实现的接口，它的文档说明如下：
A class can implement the Observer interface when it wants to be informed of changes in observable objects.
Observer中有一个update()方法：
void update(Observable o, Object arg); // Observable 是观察者 arg 是notifyObservers方法传入的参数
二、 Observable是一个被观察者继承的类，它的文档说明大致如下：
This class represents an observable object, or "data" in the model-view paradigm. It can be subclassed to represent an object that the application wants to have observed.
Observable有几个重要的方法，我们简单的介绍一下：
void addObserver(Observer o) // 加入观察者到Vetor中
protected void clearChanged() // 设置change为false
int countObservers() // 返回Vetor中观察者的数量
void deleteObserver(Observer o) // 从Vetor中删除指定的观察者
void deleteObservers() // 删除所有的观察者
void notifyObservers() // 通知Vetor中的观察者
void notifyObservers(Object arg) // 通知Vetor中的观察者，带参数
boolean hasChanged() // 判断是否发生改变
protected void setChanged() // 设置changed为true
三、 接下来，我们结合上述的例子来分析Observer的原理：
当执行MyButton button = new MyButton()，由于MyButton是继承Observable，所以下述代码会执行。
private boolean changed = false;
private Vector obs; public Observable() {
obs = new Vector();
}
当执行button.addObserver(new ClickObserver())，把参数中的Observer存放在上述初始化的Vetor中(为了适应多线程，用的是Vetor)
public synchronized void addObserver(Observer o) {
if (o == null)
throw new NullPointerException();
if (!obs.contains(o)) {
obs.addElement(o);
}
}
当执行button.process("huhx")，如果被观察者发生了改变，就通知Vetor中的观察者去执行update方法。
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);
}
使用自定义的Observer来过滤按钮监听事件
上述案例中，我们还无法做到对观察者的过滤通知，现在我们自己实现一个Observer，来对事件监听的事件过滤，更好的模拟按钮的事件机制。
一、 定义一个常量类，用于各种事件的标记：
package com.huhx.myobserver; /**
* huhx 陈慧
*/
public class Event {
// 触发所有的Listener
public static final int ALL = -1;
// 触发内部定义的Listener
public static final int DEFAULT = 0;
public static final int CLICK = 1;
public static final int PRESS = 2;
public static final int DOWN = 3;
public static final int FOCUE = 4;
}
二、 定义一个Listener接口，和Java内置的Observer作用类似，注意方法中的参数是MyObservable
package com.huhx.listener;
import com.huhx.myobserver.MyObservable;
public interface Listener {
void actionPerformed(MyObservable o, Object arg);
}
三、 定义几个实现Listener的观察者，也就是事件：
模拟点击事件：
package com.huhx.listener; import com.huhx.myobserver.MyObservable; /**
* 陈慧
* @author Linux
*
*/
public class ClickListener implements Listener {
@Override
public void actionPerformed(MyObservable o, Object arg) {
if (arg != null) {
System.out.println("click: " + arg);
} else {
System.out.println("click");
}
}
}
模拟按下事件：
package com.huhx.listener;
import com.huhx.myobserver.MyObservable;
public class PressListener implements Listener {
@Override
public void actionPerformed(MyObservable o, Object arg) {
System.out.println("press");
}
}
模拟定义在内部类中的事件：
package com.huhx.listener;
import com.huhx.myobserver.MyObservable;
public class DefaultListener implements Listener {
@Override
public void actionPerformed(MyObservable o, Object arg) {
}
}
四、 定义一个类似于Observable类的自定义被观察者：
package com.huhx.myobserver; import java.util.Vector; import com.huhx.listener.ClickListener;
import com.huhx.listener.Listener;
import com.huhx.listener.PressListener; /**
*
* @author huhx
*
*/
public class MyObservable {
private boolean changed = false;
private Vector<Listener> obs;
Object[] arrLocal; public MyObservable() {
obs = new Vector<>();
} protected synchronized void clearChanged() {
changed = false;
} public void notifyObserverByEvent(int event, Object args) {
synchronized (this) {
if (!changed)
return;
arrLocal = obs.toArray();
clearChanged();
}
notifyFixObserver(event, args);
} private void notifyFixObserver(int event, Object args) {
Listener listener = null;
for (int i = arrLocal.length - 1; i >= 0; i--) {
listener = (Listener) arrLocal[i];
switch (event) {
case Event.PRESS:
if (listener instanceof PressListener)
((PressListener) listener).actionPerformed(this, args);
break;
case Event.CLICK:
if (listener instanceof ClickListener)
((ClickListener) listener).actionPerformed(this, args);
break;
case Event.DEFAULT:
if (listener instanceof Listener)
listener.actionPerformed(this, args);
break;
case Event.ALL:
listener.actionPerformed(this, args);
break;
default:
break;
}
}
} public void notifyObserverByEvent(int event) {
notifyObserverByEvent(event, null);
} public void notifyObserverByEvent(Object args) {
notifyObserverByEvent(Event.ALL, args);
} public synchronized void addListener(Listener listener) {
if (listener == null)
throw new NullPointerException();
if (!obs.contains(listener)) {
obs.addElement(listener);
}
} protected synchronized void setChanged() {
changed = true;
}
}
五、 为了简化Button的使用，我们仿造Java中的做法，先创建一个AbstractButton，用于处理共公的代码：
package com.huhx.myobserver;
import com.huhx.listener.Listener;
public class AbstractButton extends MyObservable {
public void addListeners(Listener listener) {
addListener(listener);
}
public void process(int source, Object args) {
setChanged();
switch (source) {
case Event.CLICK:
notifyObserverByEvent(Event.CLICK, args);
break;
case Event.PRESS:
notifyObserverByEvent(Event.PRESS, args);
break;
case Event.DEFAULT:
notifyObserverByEvent(Event.DEFAULT, args);
break;
case Event.ALL:
notifyObserverByEvent(Event.ALL, args);
default:
break;
}
}
public void process(int source) {
process(source, null);
}
}
六、 创建一个被观察者，也就是我们的按钮Button
package com.huhx.myobserver; /**
*
* @author Linux
*
*/ public class MyButtton extends AbstractButton { }
七、 在测试中使用：
package com.huhx.myobserver; import com.huhx.listener.ClickListener;
import com.huhx.listener.Listener; public class PersonTest {
public static void main(String[] args) {
MyButtton buttton = new MyButtton();
buttton.addListener(new Listener() {
@Override
public void actionPerformed(MyObservable observable, Object object) {
System.out.println("listener");
System.out.println(observable + ", object: " + object.toString());
}
}); buttton.addListener(new ClickListener());
buttton.process(Event.CLICK);
// buttton.process(Event.DEFAULT, "world");
}
}
它的输出结果如下：
click: 陈慧
观察者模式的应用
一、观察者模式的优点
- 观察者和被观察者之间是抽象耦合
如此设计，则不管是增加观察者还是被观察者都非常容易扩展，而且在Java中都已经实现的抽象层级的定义，在系统扩展方面更是得心应手。
- 建立一套触发机制
根据单一职责原则，每个类的职责是单一的，那么怎么把各个单一的职责串联成真实世界的复杂的逻辑关系呢？比如，我们去打猎，打死了一只母鹿，母鹿有三个幼崽，因失去了母鹿而饿死，尸体又被两只秃鹰争抢，因分配不均，秃鹰开始斗殴，然后羸弱的秃鹰死掉，生存下来的秃鹰，则因此扩大了地盘……这就是一个触发机制，形成了一个触发链。观察者模式可以完美地实现这里的链条形式。
二、观察者模式的缺点
观察者模式需要考虑一下开发效率和运行效率问题，一个被观察者，多个观察者，开发和调试就会比较复杂，而且在Java中消息的通知默认是顺序执行，一个观察者卡壳，会影响整体的执行效率。在这种情况下，一般考虑采用异步的方式。
多级触发时的效率更是让人担忧，大家在设计时注意考虑。
三、观察者模式的使用场景
- 关联行为场景。需要注意的是，关联行为是可拆分的，而不是“组合”关系。
- 事件多级触发场景。
- 跨系统的消息交换场景，如消息队列的处理机制。