[Design Pattern]Structural Pattern-Proxy Design Pattern(代理模式)

使用時機:

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大多使用在避免未經授權,認證就對目標物件進行存取,如此一來避免資源的浪費,也對於使用者權限範圍限制.

例如:

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Facebook須登入後,才會依登入的使用者身分,給予該使用者有限的資訊擷取

class SubjectAccessor

{

 public interface ISubject

 {

  string Request ( );

 }

 private class Subject

 {

  public string Request( )

  {

   return "Subject Request " + "Choose left door\n";

  }

 }

 public class ProtectionProxy : ISubject

 {

  // An authentication proxy first asks for a password

  Subject subject;

  string password = "12345";

  public string Authenticate (string supplied)

  {

   if (supplied!=password)

    return "Protection Proxy: No access";

   else

    subject = new Subject( );

   return  "Protection  Proxy:  Authenticated";

  }

  public string Request( )

  {

   if (subject==null)

    return "Protection Proxy: Authenticate first";

   else

    return "Protection Proxy: Call to "+subject.Request( );

  }

 }

}

以上面的例子來說:
目標是要存取Subject class的物件
而要對外提供存取subject物件使用了ISubject 介面,並指定公開Request()給外部存取
為了要提供授權機制,加入了ProtectionProxy class(Proxy Pattern),並繼承ISubject實作Request(),而在讓外部存取Request()之前,要求要透過Authenticate()認證後,才實體化Subject給外部存取
而外部存取時,使用方式如下

ProtectionProxy subject = new ProtectionProxy( );

(subject  as  ProtectionProxy).Authenticate("12345");

subject.Request( );

參考書籍c#3.0 design pattern