一.关于观察者模式
1.将观察者与被观察者分离开来，当被观察者发生变化时，将通知所有观察者，观察者会根据这些变化做出对应的处理。
2.jdk里已经提供对应的Observer接口(观察者接口)与Observable(被观察者类)用于实现观察者模式
3.关于Observer接口，该接口只有一个update方法，当被观察者发生相关变化时，会通知所有的观察者，观察者接受到通知时，调用update方法进行处理。贴出源代码：
1 /* 2 * Copyright (c) 1994, 1998, Oracle and/or its affiliates. All rights reserved. 3 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. 4 * 5 * 6 * 7 * 8 * 9 *10 *11 *12 *13 *14 *15 *16 *17 *18 *19 *20 *21 *22 *23 *24 */25 package java.util;26 27 /**28 * A class can implement the <code>Observer</code> interface when it29 * wants to be informed of changes in observable s.30 *31 * @author Chris Warth32 * @see java.util.Observable33 * @since JDK1.034 */35 public interface Observer {36 /**37 * This method is called whenever the observed is changed. An38 * application calls an <tt>Observable</tt> 's39 * <code>notifyObservers</code> method to have all the 's40 * observers notified of the change.41 *42 * @param o the observable .43 * @param arg an argument passed to the <code>notifyObservers</code>44 * method.45 */46 void update(Observable o, arg);47 }
4：关于被观察者Observable的常用方法：
1. public synchronized void addObserver(Observer o)；//添加观察者对象
2. public void notifyObservers()；//通知所有观察者
3. protected synchronized void setChanged()；//设置观察项已经做出改变，此方法很重要
贴出源代码，注意内部实现：
1 /* 2 * Copyright (c) 1994, 2012, Oracle and/or its affiliates. All rights reserved. 3 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. 4 * 5 * 6 * 7 * 8 * 9 * 10 * 11 * 12 * 13 * 14 * 15 * 16 * 17 * 18 * 19 * 20 * 21 * 22 * 23 * 24 */ 25 26 package java.util; 27 28 /** 29 * This class represents an observable , or "data" 30 * in the model-view paradigm. It can be subclassed to represent an 31 * that the application wants to have observed. 32 * <p> 33 * An observable can have one or more observers. An observer 34 * may be any that implements interface <tt>Observer</tt>. After an 35 * observable instance changes, an application calling the 36 * <code>Observable</code>'s <code>notifyObservers</code> method 37 * causes all of its observers to be notified of the change by a call 38 * to their <code>update</code> method. 39 * <p> 40 * The order in which notifications will be delivered is unspecified. 41 * The default implementation provided in the Observable class will 42 * notify Observers in the order in which they registered interest, but 43 * subclasses may change this order, use no guaranteed order, deliver 44 * notifications on separate threads, or may guarantee that their 45 * subclass follows this order, as they choose. 46 * <p> 47 * Note that this notification mechanism has nothing to do with threads 48 * and is completely separate from the <tt>wait</tt> and <tt>notify</tt> 49 * mechanism of class <tt> </tt>. 50 * <p> 51 * When an observable is newly created, its set of observers is 52 * empty. Two observers are considered the same if and only if the 53 * <tt>equals</tt> method returns true for them. 54 * 55 * @author Chris Warth 56 * @see java.util.Observable#notifyObservers() 57 * @see java.util.Observable#notifyObservers(java.lang. ) 58 * @see java.util.Observer 59 * @see java.util.Observer#update(java.util.Observable, java.lang. ) 60 * @since JDK1.0 61 */ 62 public class Observable { 63 private boolean changed = false; 64 private Vector<Observer> obs; 65 66 /** Construct an Observable with zero Observers. */ 67 68 public Observable() { 69 obs = new Vector<>(); 70 } 71 72 /** 73 * Adds an observer to the set of observers for this , provided 74 * that it is not the same as some observer already in the set. 75 * The order in which notifications will be delivered to multiple 76 * observers is not specified. See the class comment. 77 * 78 * @param o an observer to be added. 79 * @throws NullPointerException if the parameter o is null. 80 */ 81 public synchronized void addObserver(Observer o) { 82 if (o == null) 83 throw new NullPointerException(); 84 if (!obs.contains(o)) { 85 obs.addElement(o); 86 } 87 } 88 89 /** 90 * Deletes an observer from the set of observers of this . 91 * Passing <CODE>null</CODE> to this method will have no effect. 92 * @param o the observer to be deleted. 93 */ 94 public synchronized void deleteObserver(Observer o) { 95 obs.removeElement(o); 96 } 97 98 /** 99 * If this has changed, as indicated by the100 * <code>hasChanged</code> method, then notify all of its observers101 * and then call the <code>clearChanged</code> method to102 * indicate that this has no longer changed.103 * <p>104 * Each observer has its <code>update</code> method called with two105 * arguments: this observable and <code>null</code>. In other106 * words, this method is equivalent to:107 * <blockquote><tt>108 * notifyObservers(null)</tt></blockquote>109 *110 * @see java.util.Observable#clearChanged()111 * @see java.util.Observable#hasChanged()112 * @see java.util.Observer#update(java.util.Observable, java.lang. )113 */114 public void notifyObservers() {115 notifyObservers(null);116 }117 118 /**119 * If this has changed, as indicated by the120 * <code>hasChanged</code> method, then notify all of its observers121 * and then call the <code>clearChanged</code> method to indicate122 * that this has no longer changed.123 * <p>124 * Each observer has its <code>update</code> method called with two125 * arguments: this observable and the <code>arg</code> argument.126 *127 * @param arg any .128 * @see java.util.Observable#clearChanged()129 * @see java.util.Observable#hasChanged()130 * @see java.util.Observer#update(java.util.Observable, java.lang. )131 */132 public void notifyObservers( arg) {133 /*134 * a temporary array buffer, used as a snapshot of the state of135 * current Observers.136 */137 [] arrLocal;138 139 synchronized (this) {140 /* We don't want the Observer doing callbacks into141 * arbitrary code while holding its own Monitor.142 * The code where we extract each Observable from143 * the Vector and store the state of the Observer144 * needs synchronization, but notifying observers145 * does not (should not). The worst result of any146 * potential race-condition here is that:147 * 1) a newly-added Observer will miss a148 * notification in progress149 * 2) a recently unregistered Observer will be150 * wrongly notified when it doesn't care151 */152 if (!changed)153 return;154 arrLocal = obs.toArray();155 clearChanged();156 }157 158 for (int i = arrLocal.length-1; i>=0; i--)159 ((Observer)arrLocal[i]).update(this, arg);160 }161 162 /**163 * Clears the observer list so that this no longer has any observers.164 */165 public synchronized void deleteObservers() {166 obs.removeAllElements();167 }168 169 /**170 * Marks this <tt>Observable</tt> as having been changed; the171 * <tt>hasChanged</tt> method will now return <tt>true</tt>.172 */173 protected synchronized void setChanged() {174 changed = true;175 }176 177 /**178 * Indicates that this has no longer changed, or that it has179 * already notified all of its observers of its most recent change,180 * so that the <tt>hasChanged</tt> method will now return <tt>false</tt>.181 * This method is called automatically by the182 * <code>notifyObservers</code> methods.183 *184 * @see java.util.Observable#notifyObservers()185 * @see java.util.Observable#notifyObservers(java.lang. )186 */187 protected synchronized void clearChanged() {188 changed = false;189 }190 191 /**192 * Tests if this has changed.193 *194 * @return <code>true</code> if and only if the <code>setChanged</code>195 * method has been called more recently than the196 * <code>clearChanged</code> method on this ;197 * <code>false</code> otherwise.198 * @see java.util.Observable#clearChanged()199 * @see java.util.Observable#setChanged()200 */201 public synchronized boolean hasChanged() {202 return changed;203 }204 205 /**206 * Returns the number of observers of this <tt>Observable</tt> .207 *208 * @return the number of observers of this .209 */210 public synchronized int countObservers() {211 return obs.size();212 }213 }
5.举一个例子吧：当婴儿哭泣时，则通知家人来哄宝宝，那么这里很明显婴儿是一个被观察者，当婴儿哭泣时，立刻通知家人(观察者)
package com.bdqn.s2.javaoop.study.proxy;import java.lang.reflect.Proxy;import java.util.Observable;import java.util.Observer;/** * 婴儿类，被观察者 */public class Baby extends Observable { private int hungry; private String name; public String getName() { return name; } public Baby(String name, int hungry) { this.hungry = hungry; this.name = name; addObserver(new Parents());//添加观察者对象，需要家长监管 } /** * 婴儿开始哭泣 */ public void cry() { if (hungry < 100) { System.out.printf("baby%s饿了，开始哭泣...%n", name); setChanged();//饥饿值过低，触发变化，此方法必须被调用 notifyObservers();//通知观察者 } }}/** * 家长，观察者 */class Parents implements Observer { @Override public void update(Observable o, arg) { if (o instanceof Baby) { Baby baby = (Baby) o; System.out.println(baby.getName()+"开始哭泣，赶紧哄宝宝啦"); } }}public class Main { public static void main(String[] args) { Baby baby = new Baby("豆豆",9); baby.cry(); }}/*输出结果baby豆豆饿了，开始哭泣...豆豆开始哭泣，赶紧哄宝宝啦*/
二 关于动态代理模式
1）代理模式是设计模式中非常常见的一种模式，这种模式可以实现对原有方法的扩展，举个例子经纪人可以替明星们办理一些事情，那么此时经纪人可以视为明星的代理。
2）代理模式可以分为静态代理和动态代理，在这里我们只对JDK提供的动态代理进行讨论。
3）由于JDK提供的代理模式所代理的类继承了Proxy，因此我们只能接口进行代理，针对类的代理可以自行参考cglib框架
4）InvocationHandler:是代理实例的调用处理程序 实现的接口。 每个代理实例都具有一个关联的调用处理程序。对代理实例调用方法时，将对方法调用进行编码并将其指派到它的调用处理程序的 invoke 方法。
//proxy:代理类，method：代理执行的方法 args:方法参数public invoke( proxy, Method method, [] args);
5）Proxy:该类主要是获取或者新创建动态代理对象
//该方法主要用于获取代理对象，注意一定是针对接口进行代理 public static newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException
6）针对上述例子进行改造：添加保姆类并改造Baby类的构造方法：
package com.bdqn.s2.javaoop.study.proxy;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.util.Observer;/** * 保姆类 */public class Nanny implements InvocationHandler { private Observer parents; public Nanny(){ parents = new Parents(); } @Override public invoke( proxy, Method method, [] args) throws Throwable { System.out.println("保姆开始照顾孩子"); = method.invoke(parents, args); return ; }}
Baby类构造函数改造：
public Baby(String name, int hungry) { this.hungry = hungry; this.name = name; addObserver((Observer) Proxy.newProxyInstance(Baby.class.getClassLoader(),new Class[]{Observer.class},new Nanny())); }
输出结果：
baby豆豆饿了，开始哭泣...保姆开始照顾孩子豆豆开始哭泣，赶紧哄宝宝啦
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