本質

分離與共享。

程式碼示例

（1）定義描述授權資料的享元介面

package flyWeight;
public interface FlyWeight {
        public boolean match(String privelage,String securEntity);
}

（2）實現享元物件

package flyWeight;
//封裝授權資料中重複出現的享元物件
public class ConcretFlyWeight implements FlyWeight {
    //內部狀態，許可權
    private String privelage;
    //內部狀態，安全實體
 

    private String securEntity;
    //傳入狀態資料，安全實體+","+許可權
    public ConcretFlyWeight(String key) {
        String[] ss = key.split(",");
        this.privelage = ss[1];
        this.securEntity = ss[0];
    }
    public String getPrivelage()
    {
        return privelage;
    }
    public String getSecurEntity
 
()
    {
        return securEntity;
    }
    @Override
    public boolean match(String privelage, String securEntity) {
        // TODO 自動生成的方法存根
        if (this.privelage.equals(privelage) && this.securEntity.equals(securEntity))
        {
            return true;
        }
        return false
 
;
    }
}

（3）提供享元工廠來負責享元物件的共享管理和對外提供享元物件的介面。

package flyWeight;

import java.util.HashMap;
import java.util.Map;

public class FlyWeightFactory {
    private  static FlyWeightFactory fwf = new FlyWeightFactory();
    private FlyWeightFactory()
    {

    }
    public  static FlyWeightFactory getInstance()
    {
        return fwf;
    }
    //快取多個FlyWeight物件
    private Map<String,FlyWeight> hm = new HashMap<>();
    public FlyWeight getFlyWeight(String key)
    {
        FlyWeight fw = hm.get(key);
        if (hm.get(key) == null)
        {
                fw = new ConcretFlyWeight(key);
                hm.put(key, fw););//這句話第一次忘寫了，導致與上篇部落格相同的結果

        }
        return fw;
    }

}

（4）使用享元物件

package flyWeight;
import java.util.HashMap;
import java.util.Map;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;

public class SecurityMsg {
//享元物件實現成單例。
    private static SecurityMsg sm = new SecurityMsg();
    private SecurityMsg()
    {

    }
    public static SecurityMsg getIntance()
    {
        return sm;
    }
    private Map<String,Collection<FlyWeight>> hMap = new HashMap<>();
    public void login(String user)
    {
        Collection<FlyWeight> cll = queryByUser(user);
        hMap.put(user,cll   }

    public boolean hasPermit(String user,String securEntity,String privilage)
    {
        Collection<FlyWeight> cll = hMap.get(user);
        if (cll == null || cll.size() == 0)
        {
            System.out.println("沒有設定"+user+"訪問許可權");
            return false;
        }
        for (FlyWeight fl:cll)
        {
            System.out.println("fl="+fl);
            if (fl.match(privilage, securEntity))
            {
                return true;
            }
        }
        return false;
    }
    //從資料庫中獲取某人所擁有的許可權
    public Collection<FlyWeight> queryByUser(String user)
    {
        Collection<FlyWeight> cl = new ArrayList<>();
        //FlyWeight fw = null;
        for (String ss:DataBuffer.cll)
        {
            String[] str = ss.split(",");
            if (str[0].equals(user))
            {
                String key = (str[1]+","+str[2]);
                 FlyWeight fw = FlyWeightFactory.getInstance().getFlyWeight(key);//這裡使用的是享元工廠建立享受元物件
                 cl.add(fw);
            }

        }
        return cl;

    }


}

（5）客戶端

package flyWeight;

public class Client {
    public static void main(String[] args)
    {
        SecurityMsg scm = SecurityMsg.getIntance();
        scm.login("張三");
        scm.login("李四");
        boolean f1 = scm.hasPermit("張三", "薪資資料", "檢視");
        //scm.login("李四");
        boolean f2 = scm.hasPermit("李四", "薪資資料", "檢視");
        System.out.println("f1="+f1);
        System.out.println("f2="+f2);
        for (int i = 0;i < 3;i++)
        {
            scm.login("張三"+i);
            scm.hasPermit("張三"+i, "薪資資料", "檢視");
        }
    }

}

執行結果：
[email protected]
[email protected]
[email protected]
f1=false
f2=true
[email protected]
[email protected]
[email protected]
很明顯，只由2個物件了。