代理模式

代理模式定义:为其他对象提供一种代理以控制对这个对象的访问.

举个栗子:小明在外打工,临近春节抢不到票,于是找到黄牛,最后黄牛'神通广大',帮他买到一张回家的火车票。

这里面黄牛就是代理角色,买票是抽象请求角色，小明是具体请求者角色。

代码清单-1 买票接口

public interface ITicketRequest {
    /**
     * 买票请求
     */
    void buyTicket();
}

代码清单-2  工人类

public class Workman implements ITicketRequest {
    private String name ;
    public Workman(String name){
        this.name = name;
    }
    
    public void buyTicket() {
        System.out.println(name+",正在买票...");
    }
    
    //此处省略name的get和set方法...
}

代码清单-3 收费接口(黄牛收费)

public interface IPay {
    /**
     * 车票代购计费
     */
    void count();
}

代码清单-4 黄牛类

public class HuangNiu implements ITicketRequest,IPay{
    private ITicketRequest ticketRequest = null;
    public  HuangNiu(ITicketRequest ticketRequest) {
        this.ticketRequest = ticketRequest;
    }


    public void buyTicket() {
        //代替小明买票
        ticketRequest.buyTicket();
        //代理的个性方法
        count();
    }
    
    public void count() {
        System.out.println("买票费用一共是: 150元");
    }
}

代码清单-5 场景类 

public class Client {

    public static void main(String[] args){
        ITicketRequest xiaoming = new Workman("小明");
        HuangNiu huangNiu = new HuangNiu(xiaoming);
        //黄牛帮小明代购火车票并收费150元
        huangNiu.buyTicket();
    }
}

以上类图关系如下:

以上为静态代理模式.

继续上面的例子,小明发现买错了票,想要退票或者改签,这时需要在"黄牛"类里面新增退票和改签方法了,那如果小明后续还需要其他功能,这个"黄牛"代理就要做新增方法改动。那有没有办法让被代理类新增方法后,代理类不需要改动呢？答案是肯定的。

动态代理模式

代码清单-6  黄牛类 －动态代理

public class HuangNiu implements InvocationHandler {
    private Object ticketRequest = null;
    public  HuangNiu(Object ticketRequest) {
        this.ticketRequest = ticketRequest;
    }


    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("*** DynamicProxyPatterns start***");
        //代替小明买票，退票，改签等操作
        method.invoke(ticketRequest, args);
        System.out.println("*** DynamicProxyPatterns end ***");
        return null;
    }

    public Object createProxyInstance(){
        ClassLoader workmanClassLoader = ticketRequest.getClass().getClassLoader();
        Class<?>[] iTicketRequestInterface = ticketRequest.getClass().getInterfaces();
        return Proxy.newProxyInstance(workmanClassLoader,iTicketRequestInterface,this);
    }

}

代码清单-7 场景类

public class Client {

    public static void main(String[] args){
        Workman xiaoming = new Workman("小明");
        HuangNiu huangNiu = new HuangNiu(xiaoming);
        //动态创建一个代理类
        ITicketRequest xiaomingProxy = (ITicketRequest)huangNiu.createProxyInstance();
        //代理类实现买票方法
        xiaomingProxy.buyTicket();
    }
}

执行结果

*** DynamicProxyPatterns start***
小明,正在买票...
*** DynamicProxyPatterns end ***