什麼是代理設計模式中的代碼的ISubject和Operation（）？

Question

我想用下面是什麼代碼就知道基地： 1. ISubject和操作（） 2. realSubject：RealSubject和 3.操作（） realSubject.Operation（） 代理設計的UML圖上模式

link

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

//PaymentProxy.java 
import java.net.*; 
import java.math.*; 
import java.rmi.*; 
     public class PaymentProxy implements PaymentService{ 
     private Payment implementation; 
     private String serviceMachine = "localhost"; 
     private String serviceName = "paymentService"; 
     public PaymentProxy() throws ServiceUnavailableException{ 
      lookupRemoteService(); 
      } 
private void lookupRemoteService() throws ServiceUnavailableException{ 
    try{ 
     String url = "//" + serviceMachine + "/" + serviceName; 
     Object lookup = Naming.lookup(url); 
      if (lookup instanceof Payment){ 
      implementation = (Payment)lookup; 
    } 
      else{ 
      throw new ServiceUnavailableException("Cannot locate remote service"); 
    } 
    } 
    catch (RemoteException exc){ 
    throw new ServiceUnavailableException("Error during remote service lookup", exc); 
    } 
    catch (NotBoundException exc){ 
    throw new ServiceUnavailableException("Remote service is not registered with naming server",  exc); 
    } 
    catch (MalformedURLException exc){ 
    throw new ServiceUnavailableException("Malformed URL for naming lookup", exc); 
    } 
    } 
     public void setServiceMachine(String machineName){ 
     serviceMachine = machineName; 
    } 
     public void setServiceName(String svcName){ 
     serviceName = svcName; 
     } 
     public void purchase(PaymentVO pay, BigDecimal price) throws PaymentException,  ServiceUnavailableException{ 
    try{ 
    if (implementation != null){ 
     implementation.purchase(pay, price); 
    } 
    } 
    catch (RemoteException exc){ 
    try{ 
     lookupRemoteService(); 
     implementation.purchase(pay, price); 
    } 
    catch (RemoteException exc2){ 
    throw new PaymentException("Cannot process payment: remote communication problems with payment service", exc2); 
    } 
    } 
    } 
    }` 

//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{ 
} 
}` 

Answer 1

的PaymentProxy應該實現Payment而不是PaymentService：

public class PaymentProxy implements Payment { 

在這種情況下：

• Payment是ISubject;
• PaymentImpl是RealSubject（所以implementation在PaymentProxy是realSubject字段）;
• 重寫purchase()方法對應於RealSubject中的Operation()。

---

更健壯的解釋：

的Payment接口由兩個類實現的。此外，它們中的每一個都會覆蓋purchase()方法。但PaymentProxy是包裝，因爲它聚合PaymentImpl並在覆蓋方法增加了空檢查：

public void purchase(PaymentVO pay, BigDecimal price) throws PaymentException,  ServiceUnavailableException, RemoteException{ 
     if (implementation != null){ 
     implementation.purchase(pay, price); 
     } 
    }