设计模式2--代理模式

代理模式（proxy）白话就是一个人替另外一个人做一些事情。

       代理模式所涉及的角色：

              i)抽象主题角色：声明了真实主题与代理主题的共同接口。

              ii)代理主题角色：包含了真实主题角色的引用，在将客户端的调用传递给真实主题角色之前或者之后调用某些

                                        方法而不是直接把调用传递给真实主题角色。

               iii)真实主题角色：定义了代理主题所代表的真实对象

      例如:

             Subject抽象类：abstract  public class Subject{

                                             abstract  public void request();

                                     }

             RealSubject类: public class RealSubject extends Subject{

                                             public void request(){

                                                    System.out.println("实现请求");

                                             }

                                     }

             ProxySubject类：public class ProxySubject extends Subject{

                                              //对真实主题的引用，用来操作真实主题

                                              private RealSubject realSubject;

                                              //请求前操作

                                              public void preRequest(){

                                                     System.out.println("请求前操作");

                                              }

                                              //请求后操作

                                              public void postRequest(){

                                                     System.out.println("请求后操作");

                                              }

                                              //实现请求方法

                                              public  void  request(){

                                                     preRequest();

                                                     if(realSubject==null){realSubject = new RealSubject();}

                                                     realSubject.request();

                                                     postRequest();

                                              }

                                      }

              客户端调用方式：Subject subject = new ProxySubject();

                                      subject.request();