Mediator Pattern

最近在K OSGi 的部份, 練習寫一些bundle 的時候影響不大, 但是當整個Project 建立在OSGi 架構上,再變成一個Web Application Bundle 時就有一些問題會出現了,有一篇文章看了一下
Soruce : ht tp://wimpi.coalevo.net/2007/09/osgi-design-practice-loose-coupling.html

Mediator 的class diagram:

Mediator這個Pattern主要在解決交錯複雜的關係,常常我們程式會有一些複雜的關係存在,若彼此都互相緊密關聯,Mediator就扮演一個中介的角色,所有人只跟Mediator溝通,Mediator負責收集所有狀態的改變,並且通知所有需要牽動的人。Mediator 有點 Facade 和 Observer 的感覺, Mediator 就像是個 Observer ，每個元件都會把 Mediator 註冊到自己本身身上，當本身有變化時，就利用已註冊在自己身上的 Mediator 去通知自己已經變化了。

看了幾個Sample 之後, 發現最多的例子都是拿一個Swing 的元件, 比如說小算盤這種元件來當例子,
最簡單的實作就是

Mediator Interface

public interface Mediator {
   public void register(String name, Colleague c);
   public void call(String name, Colleague from);
}

Mediator Implements

public class ConcreteMediator implements Mediator{
   private Hashtable<String, Colleague> colleagues = new Hashtable<String, Colleague>();

   public void register(String name, Colleague c) {
       colleagues.put(name, c);
   }
   
   public void call(String name, Colleague from) {
       Colleague c = colleagues.get(name);
       if(c!=null){
           System.out.println(from.getName() + " call " + c.getName());
       }
   }
}

Interface colleague

public interface Colleague {
   public void call(String name);
   public String getName();
}

Colleague Implements 1

public class ConcreteColleague1 implements Colleague {
   private String name = "aa";
   private Mediator med;
   
   public ConcreteColleague1(Mediator med){
       this.med = med;
       
       this.med.register(this.name, this);
   }
   
   public String getName(){
       return this.name;
   }

   public void call(String name) {
       this.med.call(name, this);
   }
}

Colleague Implements 2

public class ConcreteColleague2 implements Colleague {
   private String name = "bb";
   private Mediator med;
   
   public ConcreteColleague2(Mediator med){
       this.med = med;
       
       this.med.register(this.name, this);
   }
   
   public String getName(){
       return this.name;
   }
   

   public void call(String name) {
       this.med.call(name, this);
   }
}

Example Reference:
Wiki : http://en.wikipedia.org/wiki/Mediator_pattern
http://smartlife.blog.51cto.com/1146871/277270
http://caterpillar.onlyfun.net/Gossip/DesignPattern/MediatorPattern.htm
http://humank.wordpress.com/2011/04/19/gof-behavioral-mediator-pattern/
http://chenjumin.iteye.com/blog/640853