代理设计模式中主类的代码是什么？

Question

请帮我创建这个代理设计模式的主类？

//文件名:Payment.java

import java.math.*; import java.rmi.*;
    public interface Payment extends Remote{
    public void purchase(PaymentVO payInfo, BigDecimal price)
        throws PaymentException, RemoteException; }

//文件名：PaymentException.java

    `public class PaymentException extends Exception{
    public PaymentException(String m){
        super(m);
    }
    public PaymentException(String m, Throwable c){
        super(m, c);
    }
}`

//文件名:PaymentImpl.java

    `import java.math.*;
     import java.net.*;
     import java.rmi.*;
     import java.rmi.server.*;
           public class PaymentImpl implements Payment{
           private static final String PAYMENT_SERVICE_NAME = "paymentService";

         public PaymentImpl() throws RemoteException, MalformedURLException{
    UnicastRemoteObject.exportObject(this);
    Naming.rebind(PAYMENT_SERVICE_NAME, this);
}
public void purchase(PaymentVO payInfo, BigDecimal price)
  throws PaymentException{
}

}`

//文件名：PaymentService.java

   import java.math.*;
public interface PaymentService{
    public void purchase(PaymentVO payInfo, BigDecimal price)
      throws PaymentException, ServiceUnavailableException;
}

//文件名：PaymentVO.java

    public class PaymentVO{
}

//文件名：ServiceUnavailableException.java

public class ServiceUnavailableException extends Exception{
public ServiceUnavailableException(String m){
    super(m);
}
public ServiceUnavailableException(String m, Throwable c){
    super(m, c);
}

}

Answer 1

请参阅下面的代理设计模式类图：http://www.codeproject.com/Articles/186001/Proxy-Design-Pattern

在您的问题中，您有一个支付界面，即“主题”。然后你就有了实现 Payment 接口的 PaymentImpl，这是“真正的主题”。但是，您在这里缺少“代理”。

您需要编写一个 PaymentProxy 类，该类也将实现 Payment 接口。此类将引用“Real Subject”（PaymentImpl）类型的对象作为私有字段，并将通过此“Real Subject”对象调用从“Subject”继承的方法。

例子：

public class PaymentProxy implements Payment{

    private PaymentImpl realPayment;

    public PaymentProxy(){

    }

    public void purchase(PaymentVO payInfo, BigDecimal price) throws PaymentException{
       if(realPayment==null){
           realPayment = new PaymentImpl();
       }
       realPayment.purchase(payInfo, price);
    }
}

您可能会注意到，在使用代理设计模式时，realPayment 是按需创建的。这在对象创建成本很高时很有用。

以下是主类的代码：

public class Client{
   public static void main(String[] args){

      PaymentProxy paymentProxy = new PaymentProxy(); //note that the real proxy object is not yet created
      //... code for resolving payInfo and price as per the requirement
      paymentProxy.purchase(payInfo, price); //this is where the real payment object of type PaymentImpl is created and invoked


   }

}