有代理模式和无代理模式

Question

有人有一个通用的例子吗？通过看到这样的例子，一定会明白我们真的需要使用代理模式吗

Answer 1

当需要比简单指针更多功能或更复杂的对象引用时，代理模式就适用。下面是几种适用代理模式的常见情况：

• 控制对另一个对象的访问
• 惰性初始化
• 实现日志记录
• 方便网络连接
• 计数对对象的引用

对于一个简单的示例，让我们考虑这样一个场景：一组向导想要进入一个塔，但是有一个代理来保护资源，并且只允许前三个向导通过。

public class Wizard {

    private String name;

    public Wizard(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return name;
    }

}

public class WizardTower {

    public void enter(Wizard wizard) {
        System.out.println(wizard + " enters the tower.");
    }

}

public class WizardTowerProxy extends WizardTower {

    private static final int NUM_WIZARDS_ALLOWED = 3;

    private int numWizards;

    @Override
    public void enter(Wizard wizard) {
        if (numWizards < NUM_WIZARDS_ALLOWED) {
            super.enter(wizard);
            numWizards++;
        } else {
            System.out.println(wizard + " is not allowed to enter!");
        }
    }
}

public class App {

    public static void main(String[] args) {

        WizardTowerProxy tower = new WizardTowerProxy();
        tower.enter(new Wizard("Red wizard"));
        tower.enter(new Wizard("White wizard"));
        tower.enter(new Wizard("Black wizard"));
        tower.enter(new Wizard("Green wizard"));
        tower.enter(new Wizard("Brown wizard"));

    }
}

Red wizard enters the tower.
White wizard enters the tower.
Black wizard enters the tower.
Green wizard is not allowed to enter!
Brown wizard is not allowed to enter!

public class Wizard {

    private String name;

    public Wizard(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return name;
    }
}

public class WizardTower {

    private static final int NUM_WIZARDS_ALLOWED = 3;

    private int numWizards;

    public void enter(Wizard wizard) {
        if (numWizards < NUM_WIZARDS_ALLOWED) {
            System.out.println(wizard + " enters the tower.");
            numWizards++;
        } else {
            System.out.println(wizard + " is not allowed to enter!");
        }
    }
}

public class App {

    public static void main(String[] args) {

        WizardTower tower = new WizardTower();
        tower.enter(new Wizard("Red wizard"));
        tower.enter(new Wizard("White wizard"));
        tower.enter(new Wizard("Black wizard"));
        tower.enter(new Wizard("Green wizard"));
        tower.enter(new Wizard("Brown wizard"));
    }
}

Red wizard enters the tower.
White wizard enters the tower.
Black wizard enters the tower.
Green wizard is not allowed to enter!
Brown wizard is not allowed to enter!