代理設計模式中主類的代碼是什么？

Question

請幫助我創建此代理設計模式的主類嗎？

//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

請參閱以下類圖，了解來自以下位置的代理設計模式： http : //www.codeproject.com/Articles/186001/Proxy-Design-Pattern

在您的問題中，您有一個付款接口，即“主題”。 然后，您具有實現了Payment接口的PaymentImpl，這就是“真實主題”。 但是，您在這里缺少“代理”。

您需要編寫一個PaymentProxy類，該類還將實現Payment接口。 此類將引用作為私有字段的“真實主題”（PaymentImpl）類型的對象，並將通過此“真實主題”對象調用從“主題”繼承的方法。

范例：

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);
    }
}

您可能會注意到，使用代理設計模式時，realPayment是按需創建的。 當對象創建很昂貴時，這很有用。

以下是主類的代碼：

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


   }

}