易学设计模式六 代理模式（Proxy）
代理模式（Proxy）为另一个对象提供一个替身或占位符以控制对这个对象的访问，简而言之就是用一个对象来代表另一个对象。

public abstract class Subject {abstract public void request();}

public class RealSubject extends Subject {public void request() {System.out.println("From real subject");}}

public class ProxySubject extends Subject {private RealSubject realSubject;public ProxySubject() {realSubject = new RealSubject();}public void request() {preRequest();realSubject.request(); //输出一次realSubject.request(); //输出二次postRequest();}public void preRequest() {System.out.print("before request");}public void postRequest() {System.out.println("after request");}}

public class Client {public static void main(String[] args) {Subject subject = new ProxySubject();subject.request();}}

输出：

before requestFrom real subject
From real subject
after request

有个疑问：代理类里面输出两次才能打出真实类的一句语句，很怪，怪怪怪