<<设计模式之禅(第二版)>>——第十二

定义：

• 为其他对象提供一种代理以控制对这个对象的访问。

通用类图：

代理模式通用类图表示

/*
 * 定义一个抽象的主题类
 * */
public interface Subject {
  // 定义一个方法
  public void request();
}
public class RealSubject implements Subject {

  @Override
  public void request() {
    // 定义具体的业务逻辑

  }

}

/*
 * 实现相关的代理类
 * */
public class Proxy implements Subject {

  private Subject subject;

  public Proxy(Subject subject) {
    this.subject = subject;
  }

  @Override
  public void request() {
    // TODO Auto-generated method stub
    doBefore();
    subject.request();
    doAfter();
  }

  private void doBefore() {

  }

  private void doAfter() {

  }

}

代理模式的优点：

• 职责清晰
• 搞拓展性
• 智能化（动态代理）

代理模式的拓展：

• 普通代理模式(调用者知道代理的存在，同时知道代理的名字，但是不知道代理的是谁)：

普通代理模式类图

public interface IGamePlayer {
  void login(String user, String password);

  void killBoss();

  void upgrade();
}
public class GamerProxy implements IGamePlayer {
  private IGamePlayer gamePlayer = null;

  public GamerProxy(String name) {
    // TODO Auto-generated constructor stub
    try {
        gamePlayer = new GamerPlayer(this, name);
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
  }

  @Override
  public void login(String user, String password) {
    // TODO Auto-generated method stub
    this.gamePlayer.login(user, password);
  }

  @Override
  public void killBoss() {
    // TODO Auto-generated method stub
    this.gamePlayer.killBoss();
  }

  @Override
  public void upgrade() {
    // TODO Auto-generated method stub
    this.gamePlayer.upgrade();
  }

}

public class GamerPlayer implements IGamePlayer {

  private String name = "";

  public <T extends GamerProxy> GamerPlayer(T t, String name) throws Exception {
    // TODO Auto-generated constructor stub
    if (t == null) {
        throw new Exception("不能创建对应的用户！");
    } else {

        this.name = name;
    }

  }

  @Override
  public void login(String user, String password) {
    // TODO Auto-generated method stub
    System.out.println(user + "" + name + "" + password);
  }

  @Override
  public void killBoss() {
    // TODO Auto-generated method stub
    System.out.println(name + "killBoss");
  }

  @Override
  public void upgrade() {
    // TODO Auto-generated method stub
    System.out.println(name + "upgrade");
  }

}

• 强制代理模式（只能通过真实角色指定的代理类才能访问，也就是说由真实角色管理代理角色，即高层模块new了一个真实的对象，但是返回的确是代理角色）

强制代理模式类图

public interface IGamePlayer {
  void login(String user, String password);

  void killBoss();

  void upgrade();

  IGamePlayer getProxy();
}
public class GamerProxy implements IGamePlayer {
  private IGamePlayer gamePlayer = null;

  public <T extends GamerProxy> GamerProxy(GamerPlayer gamerPlayer) {
    // TODO Auto-generated constructor stub
    this.gamePlayer = gamePlayer;
  }

  @Override
  public void login(String user, String password) {
    // TODO Auto-generated method stub
    this.gamePlayer.login(user, password);
  }

  @Override
  public void killBoss() {
    // TODO Auto-generated method stub
    this.gamePlayer.killBoss();
  }

  @Override
  public void upgrade() {
    // TODO Auto-generated method stub
    this.gamePlayer.upgrade();
  }

  @Override
  public IGamePlayer getProxy() {
    // TODO Auto-generated method stub
    return this;
  }

}

public class GamerPlayer implements IGamePlayer {

  private String name = "";
  private IGamePlayer proxy;

  public GamerPlayer(String name)  {
    // TODO Auto-generated constructor stub
    this.name = name;
  }

  @Override
  public void login(String user, String password) {
    // TODO Auto-generated method stub
    if (isProxy()) {
        System.out.println("login");
    } else {
        System.out.println("failed");
    }
  }

  @Override
  public void killBoss() {

  }

  @Override
  public void upgrade() {

  }

  @Override
  public IGamePlayer getProxy() {
    this.proxy = new GamerProxy(this);
    return this.proxy;
  }

  private boolean isProxy() {
    if (this.proxy == null) {
        return false;
    } else {
        return true;
    }
  }
}

public class Client {
  public static void main(String[] args) {
    IGamePlayer gamer = new GamerPlayer("zhangsan");
    IGamePlayer gamerProxy = gamer.getProxy();
    gamerProxy.login("", "");
  }
}

• 增加接口整合不同的任务（图片少一个getProxy( )方法，参照上图）

多任务接口代理类整合

public interface IProxy {
  // 计算费用
  public void count();
}
public class GamerProxy implements IGamePlayer,IProxy {
  private IGamePlayer gamePlayer = null;

  public <T extends GamerProxy> GamerProxy(GamerPlayer gamerPlayer) {
    // TODO Auto-generated constructor stub
    this.gamePlayer = gamePlayer;
  }

  @Override
  public void login(String user, String password) {
    // TODO Auto-generated method stub
    this.gamePlayer.login(user, password);
  }

  @Override
  public void killBoss() {
    // TODO Auto-generated method stub
    this.gamePlayer.killBoss();
  }

  @Override
  public void upgrade() {
    // TODO Auto-generated method stub
    this.gamePlayer.upgrade();
    this.count();
  }

  @Override
  public IGamePlayer getProxy() {
    // TODO Auto-generated method stub
    return this;
  }
  @Override
  public void count() {
    // TODO Auto-generated method stub
    System.out.println("总费用");
  }
}

• 动态代理：实现阶段不用关心代理谁，而在运行阶段才指定代理哪一个对象。（面向截面编程AOP的核心，被代理类实现必须实现）

动态代理模式通用类图

public interface IAdvice {
  // 通知方法
  public void exec();
}
public class BeforeAdvice implements IAdvice {

  @Override
  public void exec() {
    // TODO Auto-generated method stub
    System.out.println("前置通知");
  }

}

public interface Subject {
  // 业务操作
  public void doSomething(String str);
}

public class ResultSubject implements Subject {

  @Override
  public void doSomething(String str) {
    // TODO Auto-generated method stub
    System.out.println("具体实际的操作方法");
  }

}

public class DynamicProxy<T> {
  public static <T> T newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h){
    //寻找JoinPoint链接点，AOP框架使用元数据定义
    if(true){
        //执行前置通知
        (new BeforeAdvice()).exec();
    }
    //执行目标，并返回结果
    return (T)Proxy.newProxyInstance(loader, interfaces, h);
  }
}
public class SubjectDynamicProxy extends DynamicProxy {//根据不同的主题进行二次封装
  public static <T> T newProxyInstance(Subject subject){
    //获取ClassLoader
    ClassLoader loader = subject.getClass().getClassLoader();
    //获取接口数据
    Class<?>[] classes = subject.getClass().getInterfaces();
    //获取handler
    DemoInvocationHandler demoIH = new DemoInvocationHandler(subject);
    
    return newProxyInstance(loader, classes, demoIH);
  }
}
public class DemoInvocationHandler implements InvocationHandler {
  // 被代理的对象
  private Object target = null;

  // 通过构造函数传递一个对象
  public DemoInvocationHandler(Object object) {
    // TODO Auto-generated constructor stub
    this.target = object;
  }

  // 代理方法
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    // TODO Auto-generated method stub
    // 被代理的方法
    return method.invoke(this.target, args);
  }

}

public class Client {//两种方式
  public static void main(String[] args) {
    // 定义主题
    Subject subject = new ResultSubject();
    // 定义主题代理类
    Subject proxy = SubjectDynamicProxy.newProxyInstance(subject);
    proxy.doSomething("");

    ///////////////////////////////////////

    // 定义主题
    Subject subjectTwo = new ResultSubject();
    // 定义handler
    InvocationHandler iH = new DemoInvocationHandler(subjectTwo);
    // 定义主题代理类
    Subject proxyTwo = DynamicProxy.newProxyInstance(subjectTwo.getClass().getClassLoader(),
            subjectTwo.getClass().getInterfaces(), iH);
    proxyTwo.doSomething("");
  }
}